diff --git a/OpenRA.Game/CPos.cs b/OpenRA.Game/CPos.cs
index cfd2cbe47d..7dcef3c928 100644
--- a/OpenRA.Game/CPos.cs
+++ b/OpenRA.Game/CPos.cs
@@ -19,23 +19,25 @@ namespace OpenRA
 	public struct CPos : IScriptBindable, ILuaAdditionBinding, ILuaSubtractionBinding, ILuaEqualityBinding, ILuaTableBinding, IEquatable<CPos>
 	{
 		public readonly int X, Y;
+		public readonly byte Layer;
 
-		public CPos(int x, int y) { X = x; Y = y; }
-		public static readonly CPos Zero = new CPos(0, 0);
+		public CPos(int x, int y) { X = x; Y = y; Layer = 0; }
+		public CPos(int x, int y, byte layer) { X = x; Y = y; Layer = layer; }
+		public static readonly CPos Zero = new CPos(0, 0, 0);
 
 		public static explicit operator CPos(int2 a) { return new CPos(a.X, a.Y); }
 
-		public static CPos operator +(CVec a, CPos b) { return new CPos(a.X + b.X, a.Y + b.Y); }
-		public static CPos operator +(CPos a, CVec b) { return new CPos(a.X + b.X, a.Y + b.Y); }
-		public static CPos operator -(CPos a, CVec b) { return new CPos(a.X - b.X, a.Y - b.Y); }
+		public static CPos operator +(CVec a, CPos b) { return new CPos(a.X + b.X, a.Y + b.Y, b.Layer); }
+		public static CPos operator +(CPos a, CVec b) { return new CPos(a.X + b.X, a.Y + b.Y, a.Layer); }
+		public static CPos operator -(CPos a, CVec b) { return new CPos(a.X - b.X, a.Y - b.Y, a.Layer); }
 		public static CVec operator -(CPos a, CPos b) { return new CVec(a.X - b.X, a.Y - b.Y); }
 
-		public static bool operator ==(CPos me, CPos other) { return me.X == other.X && me.Y == other.Y; }
+		public static bool operator ==(CPos me, CPos other) { return me.X == other.X && me.Y == other.Y && me.Layer == other.Layer; }
 		public static bool operator !=(CPos me, CPos other) { return !(me == other); }
 
-		public override int GetHashCode() { return X.GetHashCode() ^ Y.GetHashCode(); }
+		public override int GetHashCode() { return X.GetHashCode() ^ Y.GetHashCode() ^ Layer.GetHashCode(); }
 
-		public bool Equals(CPos other) { return X == other.X && Y == other.Y; }
+		public bool Equals(CPos other) { return X == other.X && Y == other.Y && Layer == other.Layer; }
 		public override bool Equals(object obj) { return obj is CPos && Equals((CPos)obj); }
 
 		public override string ToString() { return X + "," + Y; }
@@ -117,6 +119,7 @@ namespace OpenRA
 				{
 					case "X": return X;
 					case "Y": return Y;
+					case "Layer": return Layer;
 					default: throw new LuaException("CPos does not define a member '{0}'".F(key));
 				}
 			}
diff --git a/OpenRA.Mods.Common/Activities/Attack.cs b/OpenRA.Mods.Common/Activities/Attack.cs
index 09c4109161..8b450dda13 100644
--- a/OpenRA.Mods.Common/Activities/Attack.cs
+++ b/OpenRA.Mods.Common/Activities/Attack.cs
@@ -100,7 +100,9 @@ namespace OpenRA.Mods.Common.Activities
 			minRange = armaments.Max(a => a.Weapon.MinRange);
 			maxRange = armaments.Min(a => a.MaxRange());
 
-			if (!Target.IsInRange(self.CenterPosition, maxRange) || Target.IsInRange(self.CenterPosition, minRange))
+			var mobile = move as Mobile;
+			if (!Target.IsInRange(self.CenterPosition, maxRange) || Target.IsInRange(self.CenterPosition, minRange)
+				|| (mobile != null && !mobile.CanInteractWithGroundLayer(self)))
 			{
 				// Try to move within range, drop the target otherwise
 				if (move == null)
diff --git a/OpenRA.Mods.Common/Activities/Move/Move.cs b/OpenRA.Mods.Common/Activities/Move/Move.cs
index d17bcf9dac..a1360d76d8 100644
--- a/OpenRA.Mods.Common/Activities/Move/Move.cs
+++ b/OpenRA.Mods.Common/Activities/Move/Move.cs
@@ -184,10 +184,15 @@ namespace OpenRA.Mods.Common.Activities
 			else
 			{
 				mobile.SetLocation(mobile.FromCell, mobile.FromSubCell, nextCell.Value.First, nextCell.Value.Second);
-				var from = self.World.Map.CenterOfSubCell(mobile.FromCell, mobile.FromSubCell);
+
+				var map = self.World.Map;
+				var from = (mobile.FromCell.Layer == 0 ? map.CenterOfCell(mobile.FromCell) :
+					self.World.GetCustomMovementLayers()[mobile.FromCell.Layer].CenterOfCell(mobile.FromCell)) +
+					map.Grid.OffsetOfSubCell(mobile.FromSubCell);
+
 				var to = Util.BetweenCells(self.World, mobile.FromCell, mobile.ToCell) +
-					(self.World.Map.Grid.OffsetOfSubCell(mobile.FromSubCell) +
-					self.World.Map.Grid.OffsetOfSubCell(mobile.ToSubCell)) / 2;
+					(map.Grid.OffsetOfSubCell(mobile.FromSubCell) + map.Grid.OffsetOfSubCell(mobile.ToSubCell)) / 2;
+
 				var move = new MoveFirstHalf(
 					this,
 					from,
@@ -415,21 +420,22 @@ namespace OpenRA.Mods.Common.Activities
 
 			protected override MovePart OnComplete(Actor self, Mobile mobile, Move parent)
 			{
-				var fromSubcellOffset = self.World.Map.Grid.OffsetOfSubCell(mobile.FromSubCell);
-				var toSubcellOffset = self.World.Map.Grid.OffsetOfSubCell(mobile.ToSubCell);
+				var map = self.World.Map;
+				var fromSubcellOffset = map.Grid.OffsetOfSubCell(mobile.FromSubCell);
+				var toSubcellOffset = map.Grid.OffsetOfSubCell(mobile.ToSubCell);
 
 				var nextCell = parent.PopPath(self);
 				if (nextCell != null)
 				{
 					if (IsTurn(mobile, nextCell.Value.First))
 					{
-						var nextSubcellOffset = self.World.Map.Grid.OffsetOfSubCell(nextCell.Value.Second);
+						var nextSubcellOffset = map.Grid.OffsetOfSubCell(nextCell.Value.Second);
 						var ret = new MoveFirstHalf(
 							Move,
 							Util.BetweenCells(self.World, mobile.FromCell, mobile.ToCell) + (fromSubcellOffset + toSubcellOffset) / 2,
 							Util.BetweenCells(self.World, mobile.ToCell, nextCell.Value.First) + (toSubcellOffset + nextSubcellOffset) / 2,
 							mobile.Facing,
-							Util.GetNearestFacing(mobile.Facing, self.World.Map.FacingBetween(mobile.ToCell, nextCell.Value.First, mobile.Facing)),
+							Util.GetNearestFacing(mobile.Facing, map.FacingBetween(mobile.ToCell, nextCell.Value.First, mobile.Facing)),
 							moveFraction - MoveFractionTotal);
 
 						mobile.FinishedMoving(self);
@@ -440,10 +446,13 @@ namespace OpenRA.Mods.Common.Activities
 					parent.path.Add(nextCell.Value.First);
 				}
 
+				var toPos = mobile.ToCell.Layer == 0 ? map.CenterOfCell(mobile.ToCell) :
+					self.World.GetCustomMovementLayers()[mobile.ToCell.Layer].CenterOfCell(mobile.ToCell);
+
 				var ret2 = new MoveSecondHalf(
 					Move,
 					Util.BetweenCells(self.World, mobile.FromCell, mobile.ToCell) + (fromSubcellOffset + toSubcellOffset) / 2,
-					self.World.Map.CenterOfCell(mobile.ToCell) + toSubcellOffset,
+					toPos + toSubcellOffset,
 					mobile.Facing,
 					mobile.Facing,
 					moveFraction - MoveFractionTotal);
diff --git a/OpenRA.Mods.Common/Activities/Move/MoveAdjacentTo.cs b/OpenRA.Mods.Common/Activities/Move/MoveAdjacentTo.cs
index 658c43ae13..c4d05401a1 100644
--- a/OpenRA.Mods.Common/Activities/Move/MoveAdjacentTo.cs
+++ b/OpenRA.Mods.Common/Activities/Move/MoveAdjacentTo.cs
@@ -23,7 +23,7 @@ namespace OpenRA.Mods.Common.Activities
 	{
 		static readonly List<CPos> NoPath = new List<CPos>();
 
-		readonly Mobile mobile;
+		protected readonly Mobile Mobile;
 		readonly IPathFinder pathFinder;
 		readonly DomainIndex domainIndex;
 		readonly uint movementClass;
@@ -53,10 +53,10 @@ namespace OpenRA.Mods.Common.Activities
 		{
 			Target = target;
 
-			mobile = self.Trait<Mobile>();
+			Mobile = self.Trait<Mobile>();
 			pathFinder = self.World.WorldActor.Trait<IPathFinder>();
 			domainIndex = self.World.WorldActor.Trait<DomainIndex>();
-			movementClass = (uint)mobile.Info.GetMovementClass(self.World.Map.Rules.TileSet);
+			movementClass = (uint)Mobile.Info.GetMovementClass(self.World.Map.Rules.TileSet);
 
 			if (target.IsValidFor(self))
 				targetPosition = self.World.Map.CellContaining(target.CenterPosition);
@@ -91,7 +91,7 @@ namespace OpenRA.Mods.Common.Activities
 					inner.Cancel(self);
 
 				self.SetTargetLine(Target.FromCell(self.World, targetPosition), Color.Green);
-				return ActivityUtils.RunActivity(self, new AttackMoveActivity(self, mobile.MoveTo(targetPosition, 0)));
+				return ActivityUtils.RunActivity(self, new AttackMoveActivity(self, Mobile.MoveTo(targetPosition, 0)));
 			}
 
 			// Inner move order has completed.
@@ -103,7 +103,7 @@ namespace OpenRA.Mods.Common.Activities
 					return NextActivity;
 
 				// Target has moved, and MoveAdjacentTo is still valid.
-				inner = mobile.MoveTo(() => CalculatePathToTarget(self));
+				inner = Mobile.MoveTo(() => CalculatePathToTarget(self));
 				repath = false;
 			}
 
@@ -142,14 +142,14 @@ namespace OpenRA.Mods.Common.Activities
 			var loc = self.Location;
 
 			foreach (var cell in targetCells)
-				if (domainIndex.IsPassable(loc, cell, movementClass) && mobile.CanEnterCell(cell))
+				if (domainIndex.IsPassable(loc, cell, movementClass) && Mobile.CanEnterCell(cell))
 					searchCells.Add(cell);
 
 			if (!searchCells.Any())
 				return NoPath;
 
-			using (var fromSrc = PathSearch.FromPoints(self.World, mobile.Info, self, searchCells, loc, true))
-			using (var fromDest = PathSearch.FromPoint(self.World, mobile.Info, self, loc, targetPosition, true).Reverse())
+			using (var fromSrc = PathSearch.FromPoints(self.World, Mobile.Info, self, searchCells, loc, true))
+			using (var fromDest = PathSearch.FromPoint(self.World, Mobile.Info, self, loc, targetPosition, true).Reverse())
 				return pathFinder.FindBidiPath(fromSrc, fromDest);
 		}
 
diff --git a/OpenRA.Mods.Common/Activities/Move/MoveWithinRange.cs b/OpenRA.Mods.Common/Activities/Move/MoveWithinRange.cs
index 2642425392..0f68d0aa1b 100644
--- a/OpenRA.Mods.Common/Activities/Move/MoveWithinRange.cs
+++ b/OpenRA.Mods.Common/Activities/Move/MoveWithinRange.cs
@@ -11,6 +11,7 @@
 
 using System.Collections.Generic;
 using System.Linq;
+using OpenRA.Mods.Common.Traits;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Activities
@@ -31,12 +32,13 @@ namespace OpenRA.Mods.Common.Activities
 		{
 			// We are now in range. Don't move any further!
 			// HACK: This works around the pathfinder not returning the shortest path
-			return AtCorrectRange(self.CenterPosition);
+			return AtCorrectRange(self.CenterPosition) && Mobile.CanInteractWithGroundLayer(self);
 		}
 
 		protected override bool ShouldRepath(Actor self, CPos oldTargetPosition)
 		{
-			return targetPosition != oldTargetPosition && !AtCorrectRange(self.CenterPosition);
+			return targetPosition != oldTargetPosition && (!AtCorrectRange(self.CenterPosition)
+				|| !Mobile.CanInteractWithGroundLayer(self));
 		}
 
 		protected override IEnumerable<CPos> CandidateMovementCells(Actor self)
diff --git a/OpenRA.Mods.Common/Pathfinder/CellInfoLayerPool.cs b/OpenRA.Mods.Common/Pathfinder/CellInfoLayerPool.cs
index 949e7a6541..34174b6845 100644
--- a/OpenRA.Mods.Common/Pathfinder/CellInfoLayerPool.cs
+++ b/OpenRA.Mods.Common/Pathfinder/CellInfoLayerPool.cs
@@ -57,21 +57,28 @@ namespace OpenRA.Mods.Common.Pathfinder
 
 		public class PooledCellInfoLayer : IDisposable
 		{
-			public CellLayer<CellInfo> Layer { get; private set; }
 			CellInfoLayerPool layerPool;
+			List<CellLayer<CellInfo>> layers = new List<CellLayer<CellInfo>>();
 
 			public PooledCellInfoLayer(CellInfoLayerPool layerPool)
 			{
 				this.layerPool = layerPool;
-				Layer = layerPool.GetLayer();
+			}
+
+			public CellLayer<CellInfo> GetLayer()
+			{
+				var layer = layerPool.GetLayer();
+				layers.Add(layer);
+				return layer;
 			}
 
 			public void Dispose()
 			{
-				if (Layer == null)
-					return;
-				layerPool.ReturnLayer(Layer);
-				Layer = null;
+				if (layerPool != null)
+					foreach (var layer in layers)
+						layerPool.ReturnLayer(layer);
+
+				layers = null;
 				layerPool = null;
 			}
 		}
diff --git a/OpenRA.Mods.Common/Pathfinder/PathGraph.cs b/OpenRA.Mods.Common/Pathfinder/PathGraph.cs
index 2950aeb075..05bd4eda0b 100644
--- a/OpenRA.Mods.Common/Pathfinder/PathGraph.cs
+++ b/OpenRA.Mods.Common/Pathfinder/PathGraph.cs
@@ -11,7 +11,10 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using OpenRA.Mods.Common.Traits;
+using OpenRA.Primitives;
+using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Pathfinder
 {
@@ -84,12 +87,21 @@ namespace OpenRA.Mods.Common.Pathfinder
 		readonly MobileInfo mobileInfo;
 		readonly MobileInfo.WorldMovementInfo worldMovementInfo;
 		readonly CellInfoLayerPool.PooledCellInfoLayer pooledLayer;
-		CellLayer<CellInfo> cellInfo;
+		CellLayer<CellInfo> groundInfo;
+
+		readonly Dictionary<byte, Pair<ICustomMovementLayer, CellLayer<CellInfo>>> customLayerInfo =
+			new Dictionary<byte, Pair<ICustomMovementLayer, CellLayer<CellInfo>>>();
 
 		public PathGraph(CellInfoLayerPool layerPool, MobileInfo mobileInfo, Actor actor, World world, bool checkForBlocked)
 		{
 			pooledLayer = layerPool.Get();
-			cellInfo = pooledLayer.Layer;
+			groundInfo = pooledLayer.GetLayer();
+			var layers = world.GetCustomMovementLayers().Values
+				.Where(cml => cml.EnabledForActor(actor.Info, mobileInfo));
+
+			foreach (var cml in layers)
+				customLayerInfo[cml.Index] = Pair.New(cml, pooledLayer.GetLayer());
+
 			World = world;
 			this.mobileInfo = mobileInfo;
 			worldMovementInfo = mobileInfo.GetWorldMovementInfo(world);
@@ -117,7 +129,8 @@ namespace OpenRA.Mods.Common.Pathfinder
 
 		public List<GraphConnection> GetConnections(CPos position)
 		{
-			var previousPos = cellInfo[position].PreviousPos;
+			var info = position.Layer == 0 ? groundInfo : customLayerInfo[position.Layer].Second;
+			var previousPos = info[position].PreviousPos;
 
 			var dx = position.X - previousPos.X;
 			var dy = position.Y - previousPos.Y;
@@ -133,6 +146,24 @@ namespace OpenRA.Mods.Common.Pathfinder
 					validNeighbors.Add(new GraphConnection(neighbor, movementCost));
 			}
 
+			if (position.Layer == 0)
+			{
+				foreach (var cli in customLayerInfo.Values)
+				{
+					var layerPosition = new CPos(position.X, position.Y, cli.First.Index);
+					var entryCost = cli.First.EntryMovementCost(Actor.Info, mobileInfo, layerPosition);
+					if (entryCost != Constants.InvalidNode)
+						validNeighbors.Add(new GraphConnection(layerPosition, entryCost));
+				}
+			}
+			else
+			{
+				var layerPosition = new CPos(position.X, position.Y, 0);
+				var exitCost = customLayerInfo[position.Layer].First.ExitMovementCost(Actor.Info, mobileInfo, layerPosition);
+				if (exitCost != Constants.InvalidNode)
+					validNeighbors.Add(new GraphConnection(layerPosition, exitCost));
+			}
+
 			return validNeighbors;
 		}
 
@@ -179,14 +210,15 @@ namespace OpenRA.Mods.Common.Pathfinder
 
 		public CellInfo this[CPos pos]
 		{
-			get { return cellInfo[pos]; }
-			set { cellInfo[pos] = value; }
+			get { return (pos.Layer == 0 ? groundInfo : customLayerInfo[pos.Layer].Second)[pos]; }
+			set { (pos.Layer == 0 ? groundInfo : customLayerInfo[pos.Layer].Second)[pos] = value; }
 		}
 
 		public void Dispose()
 		{
+			groundInfo = null;
+			customLayerInfo.Clear();
 			pooledLayer.Dispose();
-			cellInfo = null;
 		}
 	}
 }
diff --git a/OpenRA.Mods.Common/Traits/Mobile.cs b/OpenRA.Mods.Common/Traits/Mobile.cs
index 04c6b9f081..4f2393b6e4 100644
--- a/OpenRA.Mods.Common/Traits/Mobile.cs
+++ b/OpenRA.Mods.Common/Traits/Mobile.cs
@@ -151,15 +151,17 @@ namespace OpenRA.Mods.Common.Traits
 
 		public int MovementCostForCell(World world, CPos cell)
 		{
-			return MovementCostForCell(world.Map, TilesetTerrainInfo[world.Map.Rules.TileSet], cell);
+			return MovementCostForCell(world, TilesetTerrainInfo[world.Map.Rules.TileSet], cell);
 		}
 
-		int MovementCostForCell(Map map, TerrainInfo[] terrainInfos, CPos cell)
+		int MovementCostForCell(World world, TerrainInfo[] terrainInfos, CPos cell)
 		{
-			if (!map.Contains(cell))
+			if (!world.Map.Contains(cell))
 				return int.MaxValue;
 
-			var index = map.GetTerrainIndex(cell);
+			var index = cell.Layer == 0 ? world.Map.GetTerrainIndex(cell) :
+				world.GetCustomMovementLayers()[cell.Layer].GetTerrainIndex(cell);
+
 			if (index == byte.MaxValue)
 				return int.MaxValue;
 
@@ -279,7 +281,7 @@ namespace OpenRA.Mods.Common.Traits
 
 		public int MovementCostToEnterCell(WorldMovementInfo worldMovementInfo, Actor self, CPos cell, Actor ignoreActor = null, CellConditions check = CellConditions.All)
 		{
-			var cost = MovementCostForCell(worldMovementInfo.World.Map, worldMovementInfo.TerrainInfos, cell);
+			var cost = MovementCostForCell(worldMovementInfo.World, worldMovementInfo.TerrainInfos, cell);
 			if (cost == int.MaxValue || !CanMoveFreelyInto(worldMovementInfo.World, self, cell, ignoreActor, check))
 				return int.MaxValue;
 			return cost;
@@ -413,7 +415,12 @@ namespace OpenRA.Mods.Common.Traits
 		{
 			subCell = GetValidSubCell(subCell);
 			SetLocation(cell, subCell, cell, subCell);
-			SetVisualPosition(self, self.World.Map.CenterOfSubCell(cell, subCell));
+
+			var position = cell.Layer == 0 ? self.World.Map.CenterOfCell(cell) :
+				self.World.GetCustomMovementLayers()[cell.Layer].CenterOfCell(cell);
+
+			var subcellOffset = self.World.Map.Grid.OffsetOfSubCell(subCell);
+			SetVisualPosition(self, position + subcellOffset);
 			FinishedMoving(self);
 		}
 
@@ -626,7 +633,9 @@ namespace OpenRA.Mods.Common.Traits
 
 		public int MovementSpeedForCell(Actor self, CPos cell)
 		{
-			var index = self.World.Map.GetTerrainIndex(cell);
+			var index = cell.Layer == 0 ? self.World.Map.GetTerrainIndex(cell) :
+				self.World.GetCustomMovementLayers()[cell.Layer].GetTerrainIndex(cell);
+
 			if (index == byte.MaxValue)
 				return 0;
 
@@ -716,6 +725,21 @@ namespace OpenRA.Mods.Common.Traits
 			}
 		}
 
+		public bool CanInteractWithGroundLayer(Actor self)
+		{
+			// TODO: Think about extending this to support arbitrary layer-layer checks
+			// in a way that is compatible with the other IMove types.
+			// This would then allow us to e.g. have units attack other units inside tunnels.
+			if (ToCell.Layer == 0)
+				return true;
+
+			ICustomMovementLayer layer;
+			if (self.World.GetCustomMovementLayers().TryGetValue(ToCell.Layer, out layer))
+				return layer.InteractsWithDefaultLayer;
+
+			return true;
+		}
+
 		void IActorPreviewInitModifier.ModifyActorPreviewInit(Actor self, TypeDictionary inits)
 		{
 			if (!inits.Contains<DynamicFacingInit>() && !inits.Contains<FacingInit>())
diff --git a/OpenRA.Mods.Common/Traits/World/ActorMap.cs b/OpenRA.Mods.Common/Traits/World/ActorMap.cs
index 5a942a480d..d3ffcf87e7 100644
--- a/OpenRA.Mods.Common/Traits/World/ActorMap.cs
+++ b/OpenRA.Mods.Common/Traits/World/ActorMap.cs
@@ -26,7 +26,7 @@ namespace OpenRA.Mods.Common.Traits
 		public object Create(ActorInitializer init) { return new ActorMap(init.World, this); }
 	}
 
-	public class ActorMap : IActorMap, ITick
+	public class ActorMap : IActorMap, ITick, INotifyCreated
 	{
 		class InfluenceNode
 		{
@@ -165,6 +165,8 @@ namespace OpenRA.Mods.Common.Traits
 		int nextTriggerId;
 
 		readonly CellLayer<InfluenceNode> influence;
+		readonly Dictionary<int, CellLayer<InfluenceNode>> customInfluence = new Dictionary<int, CellLayer<InfluenceNode>>();
+		public readonly Dictionary<int, ICustomMovementLayer> CustomMovementLayers = new Dictionary<int, ICustomMovementLayer>();
 
 		readonly Bin[] bins;
 		readonly int rows, cols;
@@ -192,6 +194,15 @@ namespace OpenRA.Mods.Common.Traits
 			actorShouldBeRemoved = removeActorPosition.Contains;
 		}
 
+		void INotifyCreated.Created(Actor self)
+		{
+			foreach (var cml in self.TraitsImplementing<ICustomMovementLayer>())
+			{
+				CustomMovementLayers[cml.Index] = cml;
+				customInfluence.Add(cml.Index, new CellLayer<InfluenceNode>(self.World.Map));
+			}
+		}
+
 		sealed class ActorsAtEnumerator : IEnumerator<Actor>
 		{
 			InfluenceNode node;
@@ -228,7 +239,9 @@ namespace OpenRA.Mods.Common.Traits
 			var uv = a.ToMPos(map);
 			if (!influence.Contains(uv))
 				return Enumerable.Empty<Actor>();
-			return new ActorsAtEnumerable(influence[uv]);
+
+			var layer = a.Layer == 0 ? influence : customInfluence[a.Layer];
+			return new ActorsAtEnumerable(layer[uv]);
 		}
 
 		public IEnumerable<Actor> GetActorsAt(CPos a, SubCell sub)
@@ -237,7 +250,8 @@ namespace OpenRA.Mods.Common.Traits
 			if (!influence.Contains(uv))
 				yield break;
 
-			for (var i = influence[uv]; i != null; i = i.Next)
+			var layer = a.Layer == 0 ? influence : customInfluence[a.Layer];
+			for (var i = layer[uv]; i != null; i = i.Next)
 				if (!i.Actor.Disposed && (i.SubCell == sub || i.SubCell == SubCell.FullCell))
 					yield return i.Actor;
 		}
@@ -283,7 +297,8 @@ namespace OpenRA.Mods.Common.Traits
 			if (!influence.Contains(uv))
 				return false;
 
-			return influence[uv] != null;
+			var layer = a.Layer == 0 ? influence : customInfluence[a.Layer];
+			return layer[uv] != null;
 		}
 
 		// NOTE: can not check aircraft
@@ -294,7 +309,8 @@ namespace OpenRA.Mods.Common.Traits
 				return false;
 
 			var always = sub == SubCell.FullCell || sub == SubCell.Any;
-			for (var i = influence[uv]; i != null; i = i.Next)
+			var layer = a.Layer == 0 ? influence : customInfluence[a.Layer];
+			for (var i = layer[uv]; i != null; i = i.Next)
 			{
 				if (always || i.SubCell == sub || i.SubCell == SubCell.FullCell)
 				{
@@ -318,7 +334,8 @@ namespace OpenRA.Mods.Common.Traits
 				return false;
 
 			var always = sub == SubCell.FullCell || sub == SubCell.Any;
-			for (var i = influence[uv]; i != null; i = i.Next)
+			var layer = a.Layer == 0 ? influence : customInfluence[a.Layer];
+			for (var i = layer[uv]; i != null; i = i.Next)
 				if ((always || i.SubCell == sub || i.SubCell == SubCell.FullCell) && !i.Actor.Disposed && withCondition(i.Actor))
 					return true;
 
@@ -333,7 +350,8 @@ namespace OpenRA.Mods.Common.Traits
 				if (!influence.Contains(uv))
 					continue;
 
-				influence[uv] = new InfluenceNode { Next = influence[uv], SubCell = c.Second, Actor = self };
+				var layer = c.First.Layer == 0 ? influence : customInfluence[c.First.Layer];
+				layer[uv] = new InfluenceNode { Next = layer[uv], SubCell = c.Second, Actor = self };
 
 				List<CellTrigger> triggers;
 				if (cellTriggerInfluence.TryGetValue(c.First, out triggers))
@@ -350,9 +368,10 @@ namespace OpenRA.Mods.Common.Traits
 				if (!influence.Contains(uv))
 					continue;
 
-				var temp = influence[uv];
+				var layer = c.First.Layer == 0 ? influence : customInfluence[c.First.Layer];
+				var temp = layer[uv];
 				RemoveInfluenceInner(ref temp, self);
-				influence[uv] = temp;
+				layer[uv] = temp;
 
 				List<CellTrigger> triggers;
 				if (cellTriggerInfluence.TryGetValue(c.First, out triggers))
@@ -567,4 +586,12 @@ namespace OpenRA.Mods.Common.Traits
 			}
 		}
 	}
+
+	public static class ActorMapWorldExts
+	{
+		public static Dictionary<int, ICustomMovementLayer> GetCustomMovementLayers(this World world)
+		{
+			return ((ActorMap)world.ActorMap).CustomMovementLayers;
+		}
+	}
 }
diff --git a/OpenRA.Mods.Common/Traits/World/DomainIndex.cs b/OpenRA.Mods.Common/Traits/World/DomainIndex.cs
index cf23ef6a28..73201f3b42 100644
--- a/OpenRA.Mods.Common/Traits/World/DomainIndex.cs
+++ b/OpenRA.Mods.Common/Traits/World/DomainIndex.cs
@@ -39,6 +39,11 @@ namespace OpenRA.Mods.Common.Traits
 
 		public bool IsPassable(CPos p1, CPos p2, uint movementClass)
 		{
+			// HACK: Work around units in other movement layers from being blocked
+			// when the point in the main layer is not pathable
+			if (p1.Layer != 0 || p2.Layer != 0)
+				return true;
+
 			return domainIndexes[movementClass].IsPassable(p1, p2);
 		}
 
@@ -49,6 +54,12 @@ namespace OpenRA.Mods.Common.Traits
 			foreach (var index in domainIndexes)
 				index.Value.UpdateCells(world, dirty);
 		}
+
+		public void AddFixedConnection(IEnumerable<CPos> cells)
+		{
+			foreach (var index in domainIndexes)
+				index.Value.AddFixedConnection(cells);
+		}
 	}
 
 	class MovementClassDomainIndex
@@ -119,6 +130,19 @@ namespace OpenRA.Mods.Common.Traits
 					CreateConnection(c1, c2);
 		}
 
+		public void AddFixedConnection(IEnumerable<CPos> cells)
+		{
+			// HACK: this is a temporary workaround to add a permanent connection between the domains of the listed cells.
+			// This is sufficient for fixed point-to-point tunnels, but not for dynamically updating custom layers
+			// such as destroyable elevated bridges.
+			// To support those the domain index will need to learn about custom movement layers, but that then requires
+			// a complete refactor of the domain code to deal with MobileInfo or better a shared pathfinder class type.
+			var cellDomains = cells.Select(c => domains[c]).ToHashSet();
+			foreach (var c1 in cellDomains)
+				foreach (var c2 in cellDomains.Where(c => c != c1))
+					CreateConnection(c1, c2);
+		}
+
 		bool HasConnection(int d1, int d2)
 		{
 			// Search our connections graph for a possible route
diff --git a/OpenRA.Mods.Common/TraitsInterfaces.cs b/OpenRA.Mods.Common/TraitsInterfaces.cs
index 67fea93cc4..168598488b 100644
--- a/OpenRA.Mods.Common/TraitsInterfaces.cs
+++ b/OpenRA.Mods.Common/TraitsInterfaces.cs
@@ -233,4 +233,18 @@ namespace OpenRA.Mods.Common.Traits
 
 	[RequireExplicitImplementation]
 	public interface IGainsExperienceModifier { int GetGainsExperienceModifier(); }
+
+	[RequireExplicitImplementation]
+	public interface ICustomMovementLayer
+	{
+		byte Index { get; }
+		bool InteractsWithDefaultLayer { get; }
+
+		bool EnabledForActor(ActorInfo a, MobileInfo mi);
+		int EntryMovementCost(ActorInfo a, MobileInfo mi, CPos cell);
+		int ExitMovementCost(ActorInfo a, MobileInfo mi, CPos cell);
+
+		byte GetTerrainIndex(CPos cell);
+		WPos CenterOfCell(CPos cell);
+	}
 }
diff --git a/OpenRA.Mods.Common/Util.cs b/OpenRA.Mods.Common/Util.cs
index ddbcb8a478..cbd10b5b0a 100644
--- a/OpenRA.Mods.Common/Util.cs
+++ b/OpenRA.Mods.Common/Util.cs
@@ -12,6 +12,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using OpenRA.Mods.Common.Traits;
 using OpenRA.Support;
 using OpenRA.Traits;
 
@@ -85,7 +86,13 @@ namespace OpenRA.Mods.Common
 
 		public static WPos BetweenCells(World w, CPos from, CPos to)
 		{
-			return WPos.Lerp(w.Map.CenterOfCell(from), w.Map.CenterOfCell(to), 1, 2);
+			var fromPos = from.Layer == 0 ? w.Map.CenterOfCell(from) :
+				w.GetCustomMovementLayers()[from.Layer].CenterOfCell(from);
+
+			var toPos = to.Layer == 0 ? w.Map.CenterOfCell(to) :
+				w.GetCustomMovementLayers()[to.Layer].CenterOfCell(to);
+
+			return WPos.Lerp(fromPos, toPos, 1, 2);
 		}
 
 		public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> ts, MersenneTwister random)