Chester has a long and fascinating history, dating from the arrival of the Roman army around 74 A.D. Their fortress was the stimulus for the growth of a prosperous town with such attributes of classical civilization as bathhouses, central heating, and an amphitheater. The fifth-century collapse was followed by expansion under Saxon Mercia, and the threat of Viking attack was countered by the creation of a burh. Chester prospered as an administrative and trading settlement, ultimately benefiting from commercial contacts with the Viking world. After the Norman Conquest, it became the capital of a powerful earldom and later Edward I's headquarters for his conquest of North Wales. A large abbey dominated the center and swathes of land were enclosed in friary precincts. After the Middle Ages the city lost its harbor to silting and then endured a long and damaging siege during the Civil War. It escaped full-scale industrial expansion, although it did suffer from the accompanying problems of increasing population and poor housing. Despite its varying fortunes the city has never ceased to engage in the trade and commerce that have given the place its own special identity.