The other deviation, which affects Stabian Street, can be explained on grounds of convenience. This street, which runs from the Stabian to the Vesuvius Gate, abandoned the line of the north and south streets west of it in order to take advantage of a natural depression in the hill, by following which an easy grade could be established to the higher parts of the city; that the blocks along this important thoroughfare might not be too irregular in shape, the nearest parallel streets on the east were laid out in such a way as to follow the direction of Stabian Street. The street running south from the Capua Gate resumes, with slight variation, the north and south line of Mercury Street. The public buildings of the city form two extensive groups. One group lies about the Forum (Plan II); with this we may reckon the Baths in the first block north, and the temples of Fortuna Augusta and Venus Pompeiana. The nucleus of the other is formed by the two theatres and the large quadrangular colonnade which, designed originally to afford protection for theatre-goers against the rain, was later turned into barracks for the gladiators (Plan III). There are in addition only four public buildings that need to be mentioned. Two are bathing establishments, the Stabian Baths, and those at the corner of Stabian and Nola streets. The third is a small building near the Herculaneum Gate, consisting of a hall opening on the street, with a base for a statue near the rear wall; this on insufficient grounds has been called a custom-house. The fourth, the Amphitheatre, lies in the southern corner of the city. As the public buildings were thus located in clearly defined groups, it is not probable that many yet remain in the portion of the city which has not been excavated. We may expect to find only bathing establishments, and perhaps one or two temples. There were priestesses of Ceres and of Venus, but the sanctuary of Ceres has not been discovered. Mention is made also of a priest of Mars; but the temple of Mars, according to the precept of Vitruvius (I. vii. 1) would be outside the city. A word should be added regarding the modern division of Pompeii into Regions, or wards, and Insulae. By an Insula is meant--in accordance with ancient usage--a block of houses surrounded on all sides by streets. The division into Regions was introduced by Fiorelli, and rests upon a misconception which has been corrected by more recent excavations. Fiorelli thought that the Capua Gate and the Nocera Gate were connected by a street, and that the city was thus divided by four streets (the assumed street, Stabian Street, Nola Street, and Abbondanza Street with its continuations) into nine Regions, marked on our plan with the numerals I-IX. In each Region every block, or Insula, has its number, and in the Insula a separate number is given to every door opening on a street. This arrangement is convenient because each house can be accurately designated by means of three numbers.