The Tower of the Winds is a fancy clock tower and the world’s first meteorological station. It was designed by the Macedonian astronomer Andronicus of Cyrrhus around 50 BCE. The small octagonal tower is made of Pentelic marble and stands in the Roman forum. The carved lines on the upper part of its exterior sides indicate the hours of the day with the shadow of iron rods. A water clock inside the tower showed the time when there was no sunlight. The water was piped in from a spring on the Acropolis and fed the cylindrical tank that is still visible at the back of the tower. A mechanical system regulated the flow of water inside the building; its level showed the time.