 The second important type of building that survives all over the Hellenic world is the open-air theatre, with the earliest dating from around 525–480 BC.Other architectural forms that are still in evidence are the processional gateway ("propylon"), the public square ("agora") surrounded by storied colonnade ("stoa"), the town council building ("bouleuterion"), the public monument, the monumental tomb ("mausoleum") and the "stadium".Ancient Greek architecture is distinguished by its highly formalised characteristics, both of structure and decoration.