military operations in the north of England. It was not a frontier-wall in the proper sense; on the contrary, not merely did the posts that had already from Agricola's time been pushed forward far beyond it continue to subsist by its side, but subsequently the line, about a half shorter, from the Frith of Forth to the Frith of Clyde, already occupied by Agricola with a chain of posts, was fortified in a similar but weaker way, first under Pius, then in a more comprehensive manner under Severus--as it were, as an advanced post for Hadrian's wall.[109] In point of construction this line was different from that of Hadrian only so far as it was limited to a considerable earthen wall, with fosse in front and road behind, and so was not adapted for defence toward the south; moreover, it too included a number of smaller camps. At this line the Roman imperial roads terminated,[110] and, although there were Roman posts even beyond this--the most northerly point, at which the tombstone of a Roman soldier has been found, is Ardoch, between Stirling and Perth--the limit of the expeditions of Agricola, the Frith of Tay, may be regarded as subsequently still the limit of the Roman empire. [Sidenote: Wars in the 2d and 3d centuries.] We know more of these imposing defensive works than of the application that was made of them, and generally of the later events on this distant scene of warfare. Under Hadrian a severe disaster occurred here, to all appearance a sudden attack on the camp of Eburacum, and the annihilation of the legion stationed there,[111] the same 9th legion which had fought so unsuccessfully in the war with Boudicca. Probably this was occasioned, not by a hostile inroad, but by the revolt of the northern tribes that passed as subjects of the empire, especially of the Brigantes. With this we shall have to connect the fact that the wall of Hadrian presents a front towards the south as well as towards the north; evidently it was destined also for the purpose of keeping in check the superficially subdued north of England. Under Hadrian's successor Pius also conflicts took place here, in which the Brigantes again took part; yet more exact information cannot be got.[112] The first serious attack upon this imperial boundary, and the first demonstrable crossing of the wall--doubtless that of Pius--took place under Marcus, and further attacks under Commodus; as indeed Commodus is the first emperor who assumed the surname of victory Britannicus, after the able general Ulpius Marcellus had routed the barbarians. But the sinking of the Roman power was henceforth just as apparent here as on the Danube and on the Euphrates. In the turbulent early years of Severus's reign the Caledonians had broken their promise not to interfere with the Roman subjects, and, resting on their support, their southern neighbours, the Maeates, had compelled the Roman governor Lupus to ransom captive Romans with large sums.