The amphitheatre alone was, perhaps characteristically, a building of purely Roman origin. Intended for shows and fights of gladiators and wild beasts, these were at first temporary wooden structures. The only stone predecessor to the great Flavian amphitheatre was a smaller building in the Campus Martius, the work of Statilius Taurus in 30 B.C. The Colosseum was begun by Vespasian in A.D. 72, was dedicated eight years later by Titus, and was completed by Domitian. It stands upon the site of Nero's artificial lake, is one-third of a mile in circumference, covers some 6 acres of ground, and is 160 feet in height. It could seat 87,000 spectators, and its staircases, galleries, and entrances are so admirably planned that this crowd of sight-seers must have found their seats and filed out when the show was finished with little delay and difficulty. The numbers of the entrances, cut in stone, can still be seen over each of the arches. The Colosseum is built entirely of travertine, the blocks are fitted together without mortar and are studded with holes from which the greedy despoilers of the middle ages wrenched the metal clamps. In spite of its having been used as a fortress and served as a stone quarry for centuries, it is still one of the most magnificent of the monuments of Rome. The solidity of the public buildings seems to have been in marked contrast to the flimsy nature of the common dwellings or _insulae_. In the time of Augustus these numbered 46,600, the _domui_, or houses of the rich, 1790. The former were roofed with timber or thatch. As land was dear, they were often of several stories and perilously high; many of them were built of unbaked bricks with projecting upper floors, and they were constructed with wooden framing filled in with rush and plaster, so that when a fire broke out in the city whole regions were laid waste in a few hours. As a measure of safety Augustus limited the height of the _insulae_ to 70 feet, and Trajan reduced this again to 60 feet, while a distance of 5 feet between each house was prescribed by the law of the Twelve Tables.