Occasionally a granite obelisk was brought from Thebes or Heliopolis to adorn an imperial circus. That now in the Lateran Piazza is 108 feet in height and weighs 400 tons. Ships had to be built on purpose for the task, and one of these was so enormous that after safely conveying the Vatican obelisk to Rome, it was sunk by the Emperor Claudius to serve as a breakwater for the harbour at Porto. When the laden ships arrived at the _Marmoratum_ the obelisks were hauled on shore by men and horses and then dragged and pushed on rollers along the streets by gangs of workmen. Forty-eight obelisks were once erected in Rome, of which thirty have disappeared and left no trace. [Illustration: TEMPLE OF VESPASIAN FROM THE PORTICO OF THE DII CONSENTES Built in honour of the first Flavian Emperor by his sons Titus and Domitian. The three remaining Corinthian columns are of Carrara marble. The Arch of Septimius Severus to the right was dedicated to the emperor and his sons Caracalla and Geta in A.D. 203, to commemorate their Parthian victories. It is of Pentelic marble. The church of Santa Martina in the background is near the site of the Senate House. See pages 31, 32.] While the fashion for marble lasted, no material was considered too rare or too costly. Parian marble, the most beautiful of all white marbles, from the island of Paros; Pentelic marble from Pentelicus; Hymettan marble from the mountains of Attica; rich yellow _giallo antico_ from Numidia; _cippolino_ with its beautiful green waves from Carystos; purple _pavonazzo_ from Phrygia; black marble from Cape Matapan; green and red porphyries from Egypt; alabaster from Thebes; serpentine from Sparta; jasper and fluor-spar from Asia Minor; _lapis lazuli_, with which Titus paved a chamber in his baths, from Persia, besides countless varieties of the so-called _Lumachella_ marbles and rare and beautiful _breccias_. There arose in Rome an army of marble workers, cutters and sawyers, polishers and cleaners, carvers of simple mouldings and of inscriptions, and more skilled sculptors of ornament and of statues and busts. Coloured marbles were first used in small pieces for making mosaic pavements. This art was introduced from Greece some time in the first century B.C., and in its simplest form was an arrangement of smooth pebbles in a rough pattern on a bed of cement. As the art developed, cubes, lozenges, and hexagons of travertine and grey lava were cut and fitted together in simple patterns. Then cubes of coloured marble were used, and the designs, of figures and flowers, became more elaborate. The floors were prepared with a bed of concrete, covered with several layers of cement; the last layer was carefully smoothed and levelled, and in this the cubes were fitted according to the pattern, and finally liquid cement was poured over the whole to fill in the cracks. When dry and hard the surface was polished with sand and water rubbed on with little marble blocks.