A monopteros (Ancient Greek:ὁ μονόπτερος from the Polytonic: μόνος, only, single, alone, and τὸ πτερόν, wing) is a circular colonnade supporting a roof but without any walls. Unlike a tholos (in its wider sense as a circular building), it does not have a cella. In Greek and especially Roman antiquity the term could also be used for a tholos. In ancient times monopteroi (Ancient Greek: οἱ μονόπτεροι) served inter alia as a form of baldachin for an idol. An example of this is the Monument of Lysicrates in Athens, albeit the spaces between the columns were walled in, even in ancient times. The Temple of Rome and Augustus on the Athenian Acropolis is a monopteros from Roman times with open spaces between the columns. Cyriacus von Ancona, a 15th-century traveller, handed down his architrave ins