Monopteros
A monopteros (Ancient Greek: ὁ μονόπτερος, from: μόνος, 'only, single, alone', and τὸ πτερόν, 'wing'), also called a monopteron or cyclostyle, 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 walls making a cella or room inside.