Hidden tunnel and rooms unearthed under 1,500-year-old church in Istanbul

Archaeologists excavating beneath the ruins of an early Christian church have unearthed underground rooms and a tunnel from 1,500 years ago in the oldest part of Istanbul — once Constantinople, the capital of the Byzantine Empire.

The purpose of the hidden structures isn't completely understood, but they are probably part of the vast Church of St. Polyeuctus above them, which was built when the city was the center of Christianity, the empire's official religion.

The subterranean features consist of two large chambers connected by a tunnel and seem to have been linked to the church prothesis — the chamber beside the altar where bread and wine were prepared for the Byzantine Christian rite of the Divine Liturgy, a name still used in Eastern Orthodox churches. Parts of the underground rooms are still decorated with mosaics, stone inlays and carved marble blocks, according to archaeologists.