The apse in question belongs to the collegiate church of Santa María in Calatayud, and it is one of the reasons UNESCO lists the Mudéjar architecture of Aragon as a whole. Mudéjar means the building style of Muslim craftsmen living under Christian rule after the reconquest, and in Calatayud they did wonderful things with humble brick: geometric patterns, lozenges and interlacing arches laid out in relief, glazed tiles catching the sun. Next to the apse rises an octagonal brick tower that is the town's signature, and behind it a cloister, all three named in the listing.
Calatayud itself is a town of about twenty thousand on the Jalón river, on the old road between Madrid and Zaragoza. Its name comes from the Arabic Qal'at Ayyub, Ayyub's castle, and the ridges above the town still carry the ruins of a whole complex of Moorish fortifications. A few kilometres out lie the remains of Bilbilis, the Roman town where the poet Martial was born, a man who wrote sharp, funny epigrams about life in Rome and then came home to grumble about the provinces. The old centre is a mix of fine churches, faded palaces and streets that have seen better centuries, which is part of its charm.
The A-2 motorway makes Calatayud easy to reach and easy to leave too quickly. Better to come in on the smaller roads: south toward Daroca through red clay hills and vineyards of Garnacha, or north into the Moncayo foothills where the land climbs toward the great mountain on the border with Castile. These are open, flowing roads with big skies, and the wind on the plateau can be strong, especially the cierzo, the dry north-westerly that funnels down the Ebro basin. Summer afternoons are hot and bright; winter mornings bring frost.
Fuel, food and beds are no problem here. The region's wine, from the Calatayud appellation, is mostly robust old-vine Garnacha and good value, and the local ham, roasted lamb and migas fried with garlic are made for hungry riders. Spanish folklore knows the town through the song about La Dolores, a girl from Calatayud, which locals will tell you was very unfair to her. Park near the centre, walk up to the collegiate church, and spend a few minutes on the brickwork: the more you look, the more patterns appear.