A group of unsuspecting plumbers recently uncovered a hive of ancient mikvehs in Portugal.

The plumbers were on hand to fix a water leak in an old building in the city of Coimbra. What they found instead astounded them—a cluster of 600-year-old ritual baths designed for Jewish women.

“This could be the only discovery of its kind made in Portugal,” Portuguese archaeologist Jorge Alarcao told the Publico newspaper.

“It could be the most important archeological discovery made in Coimbra over the past 70 years,” added Coimbra Mayor Manuel Machado.

The Jewish community of Coimbra dates back to the 14th century, and experts are already saying the mikvehs could predate the year 1370. Alarcao said if the dates are confirmed, the mikvehs could be among the oldest ever found in Europe.