Santa Eulalia is Mérida's local martyr — a thirteen-year-old girl tortured and killed under the persecution of Diocletian in around AD 304. The basilica built over her tomb is one of the oldest Christian sites in Spain. The current building is mainly thirteenth-century Romanesque, with a Visigothic crypt below, and underneath that, the late-Roman necropolis and the early Christian basilica where her cult began.
The basement archaeological visit, the Cripta de Santa Eulalia, is the reason to come. You walk through layered remains — Roman houses, Visigothic tombs, the first basilica's apse — with good interpretation. Outside, the Hornito de Santa Eulalia, a tiny eighteenth-century shrine, incorporates Roman columns from the Templo de Marte; the recycling of pagan stones for Christian use is again on display.