It is said that the blocks of stone in this masonry are fastened with wooden bolts made in the shape of double swallow tails, and that some of these have been found completely petrified. When the Forum was first designed Augustus encountered great opposition from owners of private house property; and through fear of the unpopularity which wholesale evictions might have caused, he accommodated the shape of the external walls to that of the ground he could occupy. Hence arose the irregular line of the exterior, which was, however, reduced to a symmetrical plan inside by secondary walls. The general shape of the interior area of the enclosure was that of a broad oblong piazza with two large semicircular side extensions or wings (somewhat like those in the Piazza S. Pietro) opposite to and corresponding to each other. The area was large, for the horse races, and games in honour of Mars were held here once when the Tiber had overflowed the circus.[77] The temple stood at the northern end between these two side extensions, and occupied about one-sixth of the whole space. Tribunals were placed in the hemicycles and courts of law held there. Some portions of the semicircular recesses are still extant by which their plan may be traced, but the outer wall is in no part preserved entire except at the back and sides of the temple. Its height at the back of the temple is 120 feet, and over the Arco dei Pantani 100 feet, which we must suppose to have been the normal height of the rest of the enclosure. These enormous walls served as a defence against fire, no less than to exclude the traffic and noise of the streets. Although it is possible that Augustus may have entertained the design of erecting a new group of public buildings as a means of gaining distinction and popularity before the battle of Philippi which established his power, yet so far as we know, the temple of Mars Ultor and the Forum Augusti owed their existence to a vow made by the emperor immediately before the decisive battle of Philippi, B.C. 42, to build if victorious a temple to Mars as the avenger of his adopted father. The dedication of the temple took place in B.C. 2, accompanied with most magnificent shows of gladiators and splendid sham sea-fights. [Sidenote: Forum of Nerva.] [Sidenote: The Colonnacce.]