An arched roof built of bricks or stone is called a vault. In the Romanesque period before the Gothic, some churches had vaulted roofs. They were always based on perfectly semi-circular shapes. There were two main ways to make a nave vault in the Romanesque period. A vault could be long like a tunnel. Churches with this type of vault were always rather dark. Or it could be square, like two tunnels crossing each other. This meant that the columns that carried the vault always had to be placed on a perfectly square ground plan, which was not always possible.