Originally, a basilica was an ancient Roman public building, where courts were held, as well as serving other official and public functions. Basilicas are typically rectangular buildings with a central nave flanked by two or more longitudinal aisles, with the roof at two levels, being higher in the centre over the nave to admit a clerestory and lower over the side-aisles. An apse at one end, or less frequently at both ends or on the side, usually contained the raised tribunal occupied by the Roman magistrates. The basilica was centrally located in every Roman town, usually adjacent to the forum and often opposite a temple in imperial-era forums. Basilicas were also built in private residences and imperial palaces and were known as "palace basilicas".