The octagonal building was built around 47 BC by the astronomer Andronicus Kyrristou. At the top of each side is a relief of wind. At the top of the roof was a bronze Triton-vane that depending on the wind seemed to trident one of the shows. Thus traders could see from the neighboring market of the wind direction to calculate the time who wanted the goods to arrive in Piraeus. On each side there was also a sundial. Inside a plumber and worked for the days it was cloudy.