Egypt, Cairo - Nilometer

This octagonal pillar is the only surviving Nilometer in Cairo, tucked away in a kiosk on the island of Roda, in the middle of the Nile. When in use, the height of water in the pit measured the annual flooding of the river. In an ideal year the water would rise to the 16th of the marked divisions (each one cubit, approximately 52cm) decorating the column.

The Nilometer is an attribute of the titular river god, Nilus (equivalent to the Egyptian deity, Hapy), and often features on coin reverses depicting Nilus.

The surrounding structure is itself of architectural significance and dates to 861 CE. Which means those pointed arches set into the walls predate the European Gothic style by around 250 years – they could be the earliest pointed arches anywhere in the world.