As near the castle site as could be, sand and lime for the mortar for the mortar were dug and burnt, lead cast and iron worked. For these castles the Normans often reused well-made Roman bricks (as at Colchester and London), and they may have made bricks of their own too. Where stone was used for the wall, solid rock, quarried flat, was preferred for the foundation; otherwise they dug deep trenches, wider than the proposed walls, and filled them with rammed stone rubble, or hardwood stakes driven into the subsoil.