Aquae Calidae, Bulgaria Aquae Calidae, Bulgaria Aquae Calidae (Latin for warm waters), also known as Therma and Thermopolis in the Middle Ages, was an ancient town in Thrace located in the territory of today's Bulgarian port city of Burgas. It was built around thermal baths using the hot springs and became one of the most important spa centres of ancient times. The site and baths of Aquae Calidae have been visited in the course of history by several important rulers from Philip II of Macedon to the Eastern Roman emperors Justinian I and Constantine IV, the Bulgarian ruler Terwel and the Ottoman Sultan
Christianity in Roman Britain introduced Roman counterparts were venerated in the region, sometimes syncretising together, as in cases like Apollo-Cunomaglus and Sulis-Minerva. Romano-British temples were sometimes erected at locations that had earlier been cultic sites in the pre-Roman Iron Age. A new style of "Romano-Celtic temple" developed which was influenced by both Iron Age and imperial Roman architectural styles but also unique from both; buildings in this style remained in use until the fourth century. The cults of various eastern deities had also been introduced to Roman Britain, among them those of the deities Isis, Mithras, and Cybele; Christianity was just one of these