diff --git a/citywalls.mss b/citywalls.mss
index afc2f96929..02ae59d17a 100644
--- a/citywalls.mss
+++ b/citywalls.mss
@@ -1,32 +1,24 @@
-/*
+#citywalls {
+  [zoom >= 14] {
+    line-color: grey;
+    line-width: 4;
+    line-opacity: 0.8;
+    [zoom >= 15] {
+      line-width: 6;
+    }
+    [zoom >= 16] {
+      line-width: 9;
+    }
+  }
+}
 
-<Style name="citywalls">
-    <Rule>
-      &maxscale_zoom14;
-      &minscale_zoom14;
-      <LineSymbolizer stroke-linejoin="round" stroke="grey" stroke-width="4" stroke-opacity="0.8"/>
-    </Rule>
-    <Rule>
-      &maxscale_zoom15;
-      &minscale_zoom15;
-      <LineSymbolizer stroke-linejoin="round" stroke="grey" stroke-width="6" stroke-opacity="0.8"/>
-    </Rule>
-    <Rule>
-      &maxscale_zoom16;
-      &minscale_zoom18;
-      <LineSymbolizer stroke-linejoin="round" stroke="grey" stroke-width="9" stroke-opacity="0.8"/>
-    </Rule>
-</Style>
-<Style name="castle_walls"> <- lines and polygons layers
-<Rule>
-      &maxscale_zoom14;
-      &minscale_zoom15;
-      <LineSymbolizer stroke="#999" stroke-width="1"/>
-    </Rule>
-    <Rule>
-      &maxscale_zoom16;
-      <LineSymbolizer stroke="#888" stroke-width="2"/>
-    </Rule>
-</Style>
-
-*/
+.castlewalls {
+  [zoom >= 14] {
+    line-color: #999;
+    line-width: 1;
+  }
+  [zoom >= 16] {
+    line-color: #888;
+    line-width: 2;
+  }
+}
diff --git a/project.mml b/project.mml
index fdf2b57d9c..0f2230a4be 100644
--- a/project.mml
+++ b/project.mml
@@ -318,7 +318,7 @@
         "dbname": "gis"
       },
       "id": "castlewalls",
-      "class": "",
+      "class": "castlewalls",
       "srs-name": "900913",
       "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
       "advanced": {},
@@ -340,7 +340,7 @@
         "dbname": "gis"
       },
       "id": "castlewalls-poly",
-      "class": "",
+      "class": "castlewalls",
       "srs-name": "900913",
       "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
       "advanced": {},