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 ...

Under a grassy field in southeastern Europe sat some mysterious ancient ruins. Archaeologists had known about the site for decades but didn’t know much about its age or purpose — until now.

The ruins are from the sixth-century church of St. Polyeuctus, which was one of the largest in Constantinople — as Istanbul was called before its conquest by Ottoman Turks in 1453.