This conically spired 25m brick tower has baffled visitors for centuries. Was it a tomb? A coronation spot? According to Iranian archaeo-astronomer Manoochehr Arian (www.jamejamshid.com), it was actually a highly sophisticated instrument for studying the stars, built in 1261 by astronomers led by Khajeh Nasir Al-Tusi (Nasruddin Tusi; 1201–74).
By design, the sun shines directly through its doors and niches on solstice and equinox days. It was possibly with data collected here, and at his more famous observatory at Maraqeh, that Tusi managed to calculate the earth’s diameter and explain discrepancies between Aristotle’s and Ptolemy’s theories of planetary movement.
The tower is in a field 3.1km east of Radkan village along 22 Bahman St. Turn at the roundabout that's marked by a mini version of the tower.