diff --git a/src/bin/tetris/main.rs b/src/bin/tetris/main.rs
index 724be0a..d7711af 100644
--- a/src/bin/tetris/main.rs
+++ b/src/bin/tetris/main.rs
@@ -3,7 +3,7 @@
 
 use games::*;
 
-// TODO: Detect when piece is going to go out of bounds and restirct parent from moving there
+// *TODO: Detect when piece is going to go out of bounds and restirct parent from moving there
 // TODO: When shape touches the rest of the pieces, re-parent to line entity
 // TODO: When line is "full" (has 10 children) clear line and add to score
 
@@ -16,7 +16,7 @@ fn main() {
             ..default()
         })
         .init_state::<Falling>()
-        .add_systems(Startup, (init_pieces, init_debug_ui))
+        .add_systems(Startup, (init_world, init_debug_ui))
         .add_systems(
             Update,
             (
@@ -40,6 +40,7 @@ fn main() {
                 sync_singleton_to_ui::<Orientation>.run_if(any_component_changed::<Orientation>),
                 check_collision.run_if(any_component_changed::<GridPosition>),
                 add_piece.run_if(not(any_with_component::<Shape>)),
+                clear_line.run_if(any_component_changed::<LineBlocks>),
             ),
         )
         .add_systems(Update, draw_grid)
@@ -81,17 +82,35 @@ impl Display for Shape {
 
 // The blocks making up this shape
 #[derive(Component)]
-#[relationship_target(relationship = BlockOf)]
+#[relationship_target(relationship = ShapeBlock)]
 struct ShapeBlocks(Vec<Entity>);
 
 /// A part of a piece, i.e., a single square of a piece
 #[derive(Component, Debug)]
 #[relationship(relationship_target = ShapeBlocks)]
-struct BlockOf {
+struct ShapeBlock {
     #[relationship]
-    parent: Entity,
+    shape: Entity,
 }
 
+// The blocks making up this shape
+#[derive(Component, Default)]
+#[relationship_target(relationship = LineBlock)]
+struct LineBlocks(Vec<Entity>);
+
+/// A part of a piece, i.e., a single square of a piece
+#[derive(Component, Debug)]
+#[require(Transform, Visibility)]
+#[relationship(relationship_target = LineBlocks)]
+struct LineBlock {
+    #[relationship]
+    line: Entity,
+}
+
+// A line holds up to 10 blocks before being cleared
+#[derive(Component, Debug)]
+struct Line(u8);
+
 // Just marks a block either of a shape or line
 #[derive(Component, Debug)]
 struct Block;
@@ -154,7 +173,7 @@ impl GridPosition {
     }
 
     fn is_colliding_with(&self, other: &Self) -> bool {
-        self.x == other.x && self.y - 1 == other.y
+        self.x == other.x && self.y.saturating_sub(1) == other.y
     }
 
     fn add_offset(&self, RelativePosition { x: x1, y: y1 }: &RelativePosition) -> Self {
@@ -263,7 +282,7 @@ struct Visuals {
     mesh: Handle<Mesh>,
 }
 
-fn init_pieces(
+fn init_world(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<ColorMaterial>>,
@@ -275,6 +294,10 @@ fn init_pieces(
         }),
         mesh: meshes.add(Rectangle::new(SCALE, SCALE)),
     });
+
+    (0..20).for_each(|i| {
+        commands.spawn((Line(i), LineBlocks::default()));
+    });
 }
 
 fn init_debug_ui(mut commands: Commands) {
@@ -442,7 +465,7 @@ fn set_piece(
             Changed<Orientation>,
         )>,
     >,
-    mut blocks: Query<&mut RelativePosition, With<BlockOf>>,
+    mut blocks: Query<&mut RelativePosition, With<ShapeBlock>>,
     mut commands: Commands,
     visuals: Res<Visuals>,
 ) {
@@ -456,7 +479,7 @@ fn set_piece(
         if blocks.is_empty() {
             commands
                 .entity(e)
-                .with_related_entities::<BlockOf>(|parent| {
+                .with_related_entities::<ShapeBlock>(|parent| {
                     positions.into_iter().for_each(|rp| {
                         parent.spawn((Mesh2d(mesh.clone()), MeshMaterial2d(mat.clone()), rp, Block));
                     });
@@ -472,6 +495,7 @@ fn set_piece(
 
 fn update_position(mut query: Query<(&GridPosition, &mut Transform), Changed<GridPosition>>) {
     query.iter_mut().for_each(|(gp, mut t)| {
+        debug_assert!(gp.x < X_MAX, "block x > x_max");
         t.translation = gp.into();
         debug!("Updating position {:?}", t.translation);
     });
@@ -548,7 +572,7 @@ fn shape_block_movement(
             Without<RelativePosition>,
         ),
     >,
-    mut blocks: Query<(&mut GridPosition, &RelativePosition), With<BlockOf>>,
+    mut blocks: Query<(&mut GridPosition, &RelativePosition), With<ShapeBlock>>,
 ) {
     shape.iter().for_each(|shape_gp| {
         blocks.iter_mut().for_each(|(mut block_gp, block_rp)| {
@@ -574,8 +598,9 @@ fn clock_cycle(n: f32) -> impl FnMut(Res<Time>, Local<f32>) -> bool {
 /// Check if the active piece is about to collide with the ground
 fn check_collision(
     active: Query<(&GridPosition, Entity), (With<Block>, With<RelativePosition>)>,
-    shape: Single<(Entity, &GridPosition), With<ShapeBlocks>>,
+    shape: Single<(&GridPosition, Entity), With<ShapeBlocks>>,
     inactive: Query<&GridPosition, (With<Block>, Without<RelativePosition>)>,
+    lines: Query<(&Line, Entity)>,
     mut commands: Commands,
 ) {
     // TODO: Easy optimizations
@@ -597,17 +622,25 @@ fn check_collision(
 
         let blocks: Vec<Entity> = active
             .iter()
-            .map(|(_, e)| commands.entity(e).remove::<RelativePosition>().id())
+            .map(|(gp, e)| commands.entity(e).remove::<RelativePosition>().id())
             .collect();
 
         debug_assert_eq!(blocks.len(), 4, "Shapes should have 4 blocks");
 
         info!("De-relating blocks {:?} and shape {:?}", blocks, *shape);
-        let (shape_e, _shape_pos) = *shape;
+        let (_shape_pos, shape_e) = *shape;
         commands
             .entity(shape_e)
-            .remove_related::<BlockOf>(blocks.as_slice())
+            .remove_related::<ShapeBlock>(blocks.as_slice())
             .despawn();
+
+        active.iter().for_each(|(GridPosition { y, .. }, block_e)| {
+            lines.iter().for_each(|(Line(i), line_e)| {
+                if *y == *i as u32 {
+                    commands.entity(line_e).add_one_related::<LineBlock>(block_e);
+                }
+            });
+        });
     }
 }
 
@@ -615,3 +648,18 @@ fn add_piece(mut commands: Commands) {
     // TODO: Choose a different piece
     commands.spawn((Orientation::default(), GridPosition::default(), Shape::T));
 }
+
+/// When a line reaches 10 blocks, clear it
+fn clear_line(
+    lines: Query<(Entity, &LineBlocks), (With<LineBlocks>, Changed<LineBlocks>)>,
+    mut commands: Commands,
+) {
+    lines.iter().for_each(|(e, lb)| {
+        if lb.0.len() == 10 {
+            commands.entity(e).despawn_related::<LineBlocks>();
+            // TODO: re-parent all blocks above this to the next line down
+            // TODO: Parent blocks to lines for movement
+
+        }
+    });
+}