The Arabian limes did not differ in its system of military defence from the limites of Europe, but whereas the European camps were originally laid down as stockaded earthworks and were not systematically clothed in stone till the time of Hadrian,[186] on the Syrian frontier the camps and forts were from the first built of solid stone masonry. The comparatively late date of the oriental defences was no doubt partially responsible for this peculiarity, but it must also be borne in mind that fortification by means of earthworks was foreign to the regions through which the Arabian limes ran. As early as the time of Vespasian, the camps of Flavius Silva at Masada, near the Dead Sea, were surrounded by walls of rudely piled stones,[187] while in the Flavian period the European camps were still fortified by earthworks and stockades. The Roman province of Arabia Petraea was created in A.D. 105, and the fortification of the first limes dates therefore from the time of Trajan. On this inner limes one great camp stands in ruins, the camp of Odhruḥ. Archaeological research on the Roman frontiers in Germany, Austria, and Britain, as well as in North Africa, has made us familiar with the general disposition of the legionary camps; moreover, we have two literary sources of information. Polybius, writing in 150 B.C., has left a description of the camp in his day, and Hyginus, writing not earlier than a period shortly before the time of Hadrian, has given an accurate account of the camp as he knew it.[188] Architecturally there is no fundamental difference between the two. The camp of Hyginus was a rectangular enclosure, with a length one-third greater than its width. It had four gateways, the Porta Praetoria and the Porta Decumana in the centre of each of the short sides, the Porta Principalis Sinistra in one of the long sides, but not in the centre, and the Porta Principalis Dextra opposite to it in the other. Round the interior of the walls lay an open space, the Intervallum. The interior area was divided by thoroughfares placed in a regular order. Between the Porta Principalis Dextra and the Porta Principalis Sinistra ran a cross street, the Via Principalis. At right angles to it, the Via Praetoria ran up to the Porta Praetoria. These two were the most important of the roads; they were wider than the others, and in the later stone-built camps they were sometimes flanked by colonnades, while at their point of junction was set a tetrapylon. The colonnades and the tetrapylon are common in cities which were laid out on the Roman camp plan.[189] Opposite the point of junction of the two streets, the centre of the camp was occupied by official and public buildings. Here lay the Forum and the Praetorium, with the Sacellum wherein the eagles of legion and cohort were deposited. Behind the Praetorium, the Via Quintana crossed the camp from side to side, while numerous small roads at right angles to it gave