diff --git a/engine/walls.go b/engine/walls.go
new file mode 100644
index 0000000..bc3a795
--- /dev/null
+++ b/engine/walls.go
@@ -0,0 +1,108 @@
+package engine
+
+import (
+	"image"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+var (
+	_ interface {
+		Collider
+		Identifier
+		Scanner
+	} = &Wall{}
+
+	_ interface {
+		Drawer
+		DrawOrderer
+		Disabler
+		Hider
+		Prepper
+		Updater
+	} = &WallUnit{}
+)
+
+// Wall is a more flexible kind of tilemap. WallUnits can be added at the same
+// level as other components and are responsible for their own drawing, so that
+// Scene can do draw ordering, e.g. hide the player character behind a wall.
+// But Wall is still responsible for collisions.
+type Wall struct {
+	ID
+	Ersatz     bool
+	Offset     image.Point //  offset the whole wall
+	Sheet      Sheet
+	UnitOffset image.Point // drawing offset
+	UnitSize   image.Point // tile size
+
+	units map[image.Point]*WallUnit
+}
+
+func (w *Wall) regUnit(u *WallUnit) {
+	if w.units == nil {
+		w.units = make(map[image.Point]*WallUnit)
+	}
+	w.units[u.Pos] = u
+}
+
+func (w *Wall) CollidesWith(r image.Rectangle) bool {
+	if w.Ersatz {
+		return false
+	}
+
+	// Probe the map at all tilespace coordinates overlapping the rect.
+	r = r.Sub(w.Offset)
+	min := div2(r.Min, w.UnitSize)
+	max := div2(r.Max.Sub(image.Pt(1, 1)), w.UnitSize) // NB: fencepost
+
+	for j := min.Y; j <= max.Y; j++ {
+		for i := min.X; i <= max.X; i++ {
+			if w.units[image.Pt(i, j)] != nil {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (w *Wall) Scan() []interface{} { return []interface{}{&w.Sheet} }
+
+// WallUnit
+type WallUnit struct {
+	Disabled
+	Hidden
+	Pos    image.Point // tilespace coordinates
+	Tile   Tile        // chooses which cell in wall.Sheet to draw
+	WallID string
+	ZOrder
+
+	wall *Wall
+}
+
+func (u *WallUnit) Draw(screen *ebiten.Image, opts ebiten.DrawImageOptions) {
+	if u.Hidden {
+		return
+	}
+	var geom ebiten.GeoM
+	geom.Translate(float2(mul2(u.Pos, u.wall.UnitSize).Add(u.wall.UnitOffset).Add(u.wall.Offset)))
+	geom.Concat(opts.GeoM)
+	opts.GeoM = geom
+
+	src := u.wall.Sheet.SubImage(u.Tile.CellIndex())
+	screen.DrawImage(src, &opts)
+}
+
+func (u *WallUnit) Prepare(g *Game) {
+	u.wall = g.Component(u.WallID).(*Wall)
+	u.wall.regUnit(u)
+}
+
+func (u *WallUnit) Update() error {
+	if u.Disabled {
+		return nil
+	}
+	if up, ok := u.Tile.(Updater); ok {
+		return up.Update()
+	}
+	return nil
+}