[Illustration: FIG. 2.--Plan of the Acropolis, &c., of Constantine’s city.] Dr. Mordtmann, by a study of the whole of the city area and its entire circumvallation as we have it to-day, in comparison with the written descriptions, has laid a firmer grasp on the problem. Labarte, he points out, was chiefly misled by a confusion of the buildings in the Forum of Constantine and those in the Forum Augusteum--a mistake elaborated in some respects by Paspates. Labarte thus placed the porphyry column of Constantine, which still marks the site of the former, together with other buildings that were quartered about it, all within the Augusteum, which last he rightly identified with the present open space to the south-west of S. Sophia. Texier, who in 1834 made a careful study of the ancient city, rightly distinguished the two fora.[14] Fig. 2 will assist in making clear our views as to the transformation of the Acropolis under Constantine. The Byzantine brick walls which now inclose the old Serai Labarte regarded as of late work, and we think the style of the building would very well bear out Paspates’ opinion that they were erected by Michael Palaeologus. The excavation for the railway exposed some remains of a wall near O in our Fig. 1 which Paspates describes as “built of large stones as much as 10 feet long by 2½ broad, and 1½ thick.”[15] The rest of the seaward wall still forming the substructure of the retaining wall of the sea-front of the old Serai, and running in a direction parallel to the Hippodrome, is also of stone. This wall is probably ancient or follows the course of the ancient Acropolis inclosure which is described by Dion Cassius as “built on rising ground and projecting into the sea.... The walls are very strong, formed of large squared stones bound together with copper, and the inside is so strengthened with earth and buildings that the whole seems one thick wall.”[16]