in different provinces of the empire. It is clear that such a well-manned outpost was not intended merely for defense; it was used to attack the hostile northern tribes. Moreover, Hadrian’s Wall identified Rome by creating a highly visible boundary. Because traders had to use the milecastles as crossing points to the unconquered territories beyond, and because there was a concentration of population, markets and other social structures developed in some areas. Hadrian was succeeded by Antoninus Pius, who in a.d. 139 commanded another advance into Scotland, reestablishing the frontier. The 37-mile-long (59-kilometer) Antonine Wall was built around a.d. 142 between what is now Old Kilpatrick on the Clyde River and Carriden on the Forth. The 9-foot-high (2.75-meter) turf-faced soil rampart stood on a stone foundation. There was a 40-foot-wide (12-meter) vallum, 12 feet (3.7 meters) deep on its north side. Small forts were located at about 400-yard (370-meter) intervals.

By about a.d. 155 the Romans again retreated from Scotland, to return only briefly between a.d. 159 and 163. Hadrian’s Wall regained its former importance; the vallum, which had been partially filled, was finally reconstructed by about a.d. 208. Breached only three times during the remainder of the occupation—in a.d. 197, 296, and 367—it was retaken on each occasion and rebuilt where necessary to remain the frontier of Roman Britain until the last legions departed in a.d. 410.

Further reading

Bruce, J. Collingwood. 1978. Handbook to the Roman Wall, with the Cumbrian Coast and Outpost Forts. Newcastle upon Tyne, UK: H. Hill.

Divine, David. 1969. Hadrian’s Wall: A Study of the North-West Frontier of Rome. Boston: Gambit.

Shotter, David. 1996. The Roman Frontier in Britain: Hadrian’s Wall, the Antonine Wall, and Roman Policy in the North. Preston. UK: Carnegie.

Hagia Sofia

Istanbul, Turkey

The great Church of the Holy Wisdom, known as Hagia Sofia or Sancta Sofia, in Istanbul, is the high point of Byzantine ecclesiastical architecture, remarkable for its revolutionary dynamic structural system and the ingenuity of a plan that subordinates liturgy to form. It was dedicated by the Byzantine emperor Justinian in December 537. Like many churches, it was built on the site of former sacred structures, some of which predated Christianity. The earliest church had been replaced in 361 by the timber-roofed basilica Megala Ekklesia. Damaged during religious riots in 404, this second building was restored eleven years later under Emperor Theodosius II, only to be burned down in another uprising in 532. Within weeks Justinian commissioned the great church of Hagia Sofia.

He had been, crowned in 527. Despite the fall of the Western Empire to Germanic invaders in the late fifth century, Justinian ensured that his Eastern Empire survived. He and his wife, Theodora, reigned as unofficial joint rulers, together transforming Constantinople into a city that was universally admired and envied. Justinian employed the architects Anthemios of Tralles and Isidor of Miletus to build a church of great size and magnificence, sparing no expense. Materials were transported from all over his domain. Dressed marble was plundered from classical pagan buildings; it is said that eight red porphyry columns were brought from the Artemiseion at Ephesus; new stone came from the finest marble quarries in Phrygia, Egypt, Thessaly, and the Morean Peninsula. The interiors were decorated with mosaics of gold, silver, glass, marble, and granite tesserae. Because of the urgency, tradition has it, 1,000 masons and 10,000 apprentices worked on the building. It was completed in just twenty days under five years. There is a story, perhaps apocryphal, that upon, first visiting the completed church Justinian exclaimed. “Oh Solomon! I have excelled you!”

The central dome, framed with forty brick ribs, is slightly elliptical, its base measuring 101 by 104 feet (30.3 by 31.2 meters). It springs from pendentives at 183 feet (54 meters) above the floor and rises to 226 feet (67.8 meters). There is a window between the bases of each pair of ribs, and the resulting ring of light creates the illusion that the dome is poised in the air with little apparent support. The true massiveness of the masonry structure is replaced with a virtual building created from light—not only because