Bearing in mind the styles of construction just described, we may now turn to the architectural history of Pompeii, which, as we shall see, falls naturally into six periods. The first period is that to which the Doric temple in the Forum Triangulare and the city walls belong. From the style of the temple, we may safely conclude that it was built in the sixth century B.C.; the evidence is too scanty to enable us definitely to fix the date of the walls. The building materials used were the Sarno limestone and gray tufa. The second period may be designated as the Period of the Limestone Atriums, so characterized from the peculiar construction of a number of houses found in different parts of the city. On the side facing the street these houses have walls of ashlar work of Sarno limestone (Fig. 10), but the inner walls are of limestone framework (Fig. 9). [Illustration: Fig. 10.--Façade of Sarno limestone, house of the Surgeon.] Almost no ornamental forms belonging to this period have come down to us; so far only a single column has been found, built into the wall of a house. It is of the Doric style, and once formed part of a portico that ran along the west side of the small open space at the northwest corner of Stabian and Nola streets; it is thus the sole remnant of a public building. In the only complete house that has survived from this period, the house of the Surgeon, there was a portico in front of the garden, but the roof was supported by square pillars, not by columns. There is no trace of wall painting. Characteristic as the construction of the limestone atriums is, it is difficult to determine to what age they belong. The beginning of the period cannot be determined even approximately. The end, however, is fixed by the earlier limit of the next period, the Second Punic War. We may, therefore, assign the houses with the limestone atriums to a period just preceding this war; reckoning in round numbers, they were built before 200 B.C. In the third, or Tufa Period, came the climax of the development of Pompeian architecture prior to the Roman domination. The favorite building material was the gray tufa. With the exception of the Greek temple mentioned above, all the public buildings of Pompeii that do not belong to the time of the Roman colony have a homogeneous character; a list of them would include the colonnade about the Forum, the Basilica, the temples of Apollo and of Jupiter, the Large Theatre with the colonnades of the Forum Triangulare and the Barracks of the Gladiators, the Stabian Baths, the Palaestra, and the outer part of the Porta Marina with the inner parts of the other gates. Closely associated with these public edifices is a large number of private houses; as a specially characteristic example, we may mention the house of the Faun.