porto, portugal (ap) | A chance discovery during renovations of a building in the Atlantic port city of Porto has revealed a dark secret from Portugal’s past: a 16th-century synagogue.

Built at a time when Portugal’s Jews had been forced to convert to Catholicism or risk being burned at the stake, the house of worship was hidden behind a false wall in a four-story house that Father Agostinho Jardim Moreira, a Roman Catholic priest, was converting into a home for his old-age parishioners.

A scholar of Porto’s Jewish history, he says that as soon as the workers told him of the wall, “I knew there had to be some kind of Jewish symbol behind it.”

His hunch was confirmed when the wall came down to reveal a carved granite repository, about 5 feet tall, arched at the top and facing east toward Jerusalem.

It was the ark where the medieval Jews kept their Torah scrolls.

Pieces of decorative green tiles in the ark further confirmed the age of the ark when experts dated their glazing to a method used in the 16th century.

Only two other arks from the period have been found in Portugal, and last month the Portuguese Institute of Architectural Heritage authenticated this one as the third.