When Luigi Maria Calio, a classical archaeology professor, first brought students from the University of Catania to excavate an area of Ostia Antica, the ancient commercial port of call outside Rome, he wasn’t sure what he might find, the New York Times said. The dig site had not been explored in modern times, in spite of its central location next to a square that was once the city’s headquarters for shippers and traders and is today renowned for its mosaics.

“We thought we’d find some warehouses or a fluvial port,” he said. Instead, the archaeologists last summer uncovered what may be the oldest existing example in the ancient Roman world of a mikvah, a Jewish ritual bath. They have tentatively dated the structure to the late fourth or early fifth century.

“Such an antique mikvah has never been found outside Israel, “so it’s a very relevant find,” said Riccardo Di Segni, Rome’s chief rabbi. He added that the discovery has contributed to illuminating the rich history of Jews in Rome land Ostia Antica.