These were originally called tekhenu by their builders, the Ancient Egyptians, and were believed to have been constructed around 3500 BC. They were tall rectangular structures which would cast shadows to help divide the day into sections. They were geographically located in certain places. The obelisks were pointed, and as the sun moved, they cast a large shadow on the ground. The path of the shadow could be mapped out with intervals that represented the hours of the day.