The triangular building is considered to be the oldest intact Gothic monument of the medieval town of Greifensee.

Originally, it was integrated into the eastern corner of the city walls as a Wehrkirche, a fortified church, repeating in its ground floor the plan of the small town.

The Gothic building got its unusual floor plan due to the inclusion in the town walls of Greifensee.

The interior has a single central pillar, which unfolds to a stellar vault with magnificent keystones.

For centuries, the tiny Gallus chapel has been the Parish church of the medieval town of Greifensee.