The Nabão (Portuguese pronunciation: [nɐˈbɐ̃w̃]) is a river in Portugal. It rises in Ansião and passes through the city of Tomar before joining the Zêzere River — a course of about 66 kilometres (41 mi). It was known to the Romans as Nabanus. Before entering the territory of Tomar it has his biggest source in a place called Agroal.