© 1982 Erich Lessing/Culture and Fine Arts Archives

Nilometer: Measuring the depth of the Nile in the fifth century was often done with a Nilometer. This round tower-like instrument with a conical roof is divided by horizontal lines into stories numbered from six to ten in Greek; this type of Nilometer could have been used to measure the water level of the Sea of Galilee. The Nilometer is the only architectural form in the extant mosaic of the church’s right transept; all around it flutter a marshland profusion of birds and flowers.