A small chapel, rectangular in shape, with a tunnel vault roof. The archbishop of Tarragona authorised its construction in 1369 and devoted it to Saint Valerius. It served the small population of Formentera, which had been reduced in 1348 due to the Black Death. During the 18th century, when the island was repopulated, the Saint Valerius chapel was joined to a new house called Sa Tanca Vella, which gives the building its current name. In the early 1980s the house, in ruins, was demolished to restore the chapel, which was purchased by the Formentera Council in 1983. It was declared site of cultural interest in 1993 and is located in the protected area of Sant Francesc Xavier´s historical complex.