the roman bricks used for building walls are often referred to as 'tiles', because they are rather thin, flat squares, made in standard sizes, often related to the roman foot ( ), from around 20 cm to about 58 cm square, and about 5–7 cm thick. even stone-built walls frequently incorporated horizontal tile-courses. brick-built walls were finished with various types of facing, rendering or plastering on both exterior and interior surfaces, so that the bricks themselves were not visible.