The frieze of the tower showing the Greek wind gods Boreas (north wind, on the left) and Skiron (northwesterly wind, on the right).

The Tower of the Winds, also called horologion (timepiece), is an octagonal Pentelic marble tower on the Roman agora in Athens. It was supposedly built by Andronicus of Cyrrhus around 50 BC, but according to other sources might have been constructed in the 2nd century BC before the rest of the forum.

The 12 m tall structure has a diameter of about 8 m and was topped in antiquity by a weathervane-like Triton that indicated the wind direction. Below the frieze depicting the eight wind deities — Boreas (N), Kaikias (NE), Eurus (E), Apeliotes (SE), Notus (S), Lips (SW), Zephyrus (W), and Skiron (NW) — there are nine sundials. In its interior, there was a water clock (or clepsydra), driven by water coming down from the Acropolis.

In early Christian times, the building was used as the bell tower of a Byzantine Church. It was partly buried in the ground until it was fully excavated in the 19th century by the Greek Archaeological Society .