The object of the great system of Roman roads was purely military.[9] Along these broad paved “streets” the troops from the various stations could be mobilised with great quickness. They kept as a rule to high ground, choosing a convenient ridge, like that which runs from end to end of Lincolnshire, and preserving as straight a line as possible. The most important stations were placed at the crossing of rivers or at the junction of roads. In the early days of the Roman occupation, the operations of the army were directed entirely against the native tribes. No system of coast defence was adopted. The necessity for this came later, when Britain, under Roman dominion, was attacked by bodies of Saxon pirates. A chain of fortresses was then constructed along what was known as the Saxon shore, from Branodunum (Brancaster) in north Norfolk to Portus Adurni in Sussex or Hampshire. The remains of the walls of Gariannonum (Burgh Castle in Suffolk), Rutupiae (Richborough in Kent), Anderida (Pevensey in Sussex), and Portus Magnus (Porchester in Hampshire), are, next to the great wall, perhaps the most interesting relics of the Roman epoch which we possess. The forts of the Saxon shore were placed, for the most part, at the mouths of estuaries, for which the foreign pirates would naturally make. [Illustration: Cilurnum] In several cases a Roman station was founded on the site of a British settlement. It was, however, more compact in plan, and occupied only a portion of the site. The earthworks defending the west side of the settlement which preceded Camulodunum (Colchester) are two to three miles beyond the Roman wall of the city, which occupied merely the north-east angle of a very large and straggling enclosure. The original Roman station at Lincoln may be taken as a typical example of a walled town of this epoch.[10] It was a rectangular enclosure, with its longer axis from east to west, occupying the south-west angle of the high ridge above the valley of the Witham. In each of the four walls was a gateway. The inner arch and the postern, with part of the side walls, of the northern gateway still remain, and of the southern gateway there are still substantial fragments; the line of the street which led from one to the other is still fairly, though not accurately, preserved. The positions of the east and west gateways are known: the line of the street from the east gate to the centre of the city was deflected in the middle ages, but its continuation to the west gate is represented by the course of a street, much widened in modern times. Close to the meeting of the four streets was the market-place or _forum_. This, in the early days of Roman Lincoln, was the _praetorium_, or military headquarters of the camp. But the legion quartered at Lincoln was removed to York, as it seems, in the time of Vespasian, and the city settled down to a civil and commercial existence. Round the _forum_ were clustered the chief public buildings of the city, and the