Tucked away in the hills outside Coimbra lie a network of schist villages. Originally built to house shepherds and animals during the summer grazing season, these houses rise up in tawny browns and tans, almost indistinguishable from the rocks that surround them.

They are made of schist rock, thinly layered, like sheets of phyllo pastry, and some of the oldest have no mortar at all between the stones.