The Tower of the Winds (or the Horologion of Andronikos of Kyrrhos), is a tall, octagonal building immediately east of the Roman Agora. It was designed by a famous astronomer (Andronikos of Cyrrhus) to be an elaborate water clock (on the inside), sundial (on the outside), and weathervane (on the top).
The nickname "Tower of the Winds" is derived from the personifications of the 8 winds carved on the 8 sides of the building. Scholars used to think that the Tower of the Winds was built in the 1st century B.C. (that is, during the early Roman empire), but many archaeologists now prefer a construction date in the mid-2nd century B.C. (during the Hellenistic period).
Texts and images sources: https://www.wikipedia.org/, https://www.visitgreece.gr/