Kasım Ağa Mosque, Istanbul

Kasım Ağa Mosque is a house of worship with a square floor plan that combines brick and stone in Byzantine fashion, oriented east to west. The interior consists of a single large space without divisions.

The building started as a Christian church in the 10th century and underwent transformation into a mosque through a conversion process. This change took place in the early 16th century under Kasım Bey bin Abdullah.

The mosque demonstrates how Byzantine architecture continues in Istanbul's religious life, showing continuity between ancient building methods and Islamic practices. Visitors can see this connection in the simple stone walls and basic room layout.

The building sits near the ancient Charisius Gate between Chora Church and Fethiye Mosque and is easy to reach. Visitors should keep in mind it is an active place of prayer and respect for the community's practices matters.

The walls of the structure show traces of different building phases that reveal both Byzantine and Ottoman craftsmanship techniques. These visible layers tell a story of nearly a thousand years of urban change.