M. Blanchet, writing of the walls of the cities of Gaul, says: “Often the curtains are not bonded with the towers. This independence reminds one of a precept of Philo’s, which advises that the method should be followed so as to prevent the consequences of unequal settlement between the two. But there is a more simple explanation—the town under immediate danger ensures itself first with the curtain and adds the towers after. Most of the fortifications are those which the Romans built on the approach of the Barbarian invasions. To this period belong the walls of Rome and those of the cities of Gaul.” Choisy again has an interesting account of the towers of the walls of Constantinople, with a diagram of arches in the sides of the towers at the ground level, which were built so that the effective part of their foundations should be kept clear of the wall. Now, the foundations of the London bastions provide evidence of a similar way of thinking. [Illustration: FIG. 31. ] In Fig. 31 I give a sketch of this angle bastion made on July 5, 1909. Here is seen the City Wall curving round from the north to the west, and against it the bastion. The Roman wall was badly cracked and leaning outward (A); in the corner by the bastion the plinth and the foundation are seen, and below a sloping bank of wet clay (C), and farther out water (W). The bastion was built of rubble, and was hollow to the base; the form was different below and above (see B). In the sketch the tile courses are seen going through the thickness of the wall. The bastions which have been most carefully examined are those on the site of the General Post Office, described in _Archæologia_, lxiii. (1912). One is said to have been built in “the usual manner of random rubble”; it was separate from the City Wall, and the foundation was deeper than that of the wall. A second was built in a very soft spot. “Why it should have been selected is not easy to see, as at a little distance either way the builders could have found firm soil.” Its site was an old stream bed, and the conditions might well be the cause of a settlement at the point. This, as suggested above, may have been the reason the bastion was erected just here. (For the bastion by Giltspur Street, see _S. A. Proceedings_, 2 S. xxii. 476.) [Illustration: FIG. 32. ]