Welcome to the Greater Synagogue of Barcelona, once the heart of Jewish life in the city. Tucked into the Call Mayor, the medieval Jewish quarter, it’s considered one of the oldest synagogues in Europe. Curious how old? The structure includes remnants of Roman walls built in opus africanum—a masonry style using alternating vertical and horizontal stone blocks. This has led some to believe the building dates back to Roman times. Was it always a synagogue? We can’t say for sure—but its layout matches instructions in the Tosefta, a collection of Jewish oral laws: an eastward-facing façade toward Jerusalem, and two windows to let light in. In fact, its orientation defies the Roman grid of Barcino, which ran northwest to southeast—another clue to its sacred purpose. It served as a synagogue until at least the late 14th century. Want to know what happened next? Let’s find out.