The case is quite different with regard to the eastern and northern frontiers, on which the really greatest changes took place, and where Germany, as Germany, made its greatest advances. ♦Advance of the Empire.♦ Along this line the Roman Empire and the German Kingdom meant the same thing. On this side the frontier had to be marked, so far as it could be marked, against nations which had had nothing to do with the elder Empire. Here then for many ages the Roman Terminus advanced and fell back according to the accidents of a long warfare. The whole frontier of the kingdom towards its northern and eastern neighbours was defended by a series of _marks_ or border territories whose rulers were clothed with special powers for the defence and extension of the frontier.[13] They had to guard the realm against the Dane in the north, and against the Slave during the whole remaining length of the eastern frontier, except where, in the last years of the ninth century, the Magyar thrust himself in between the northern and southern Slaves. ♦Hungarian frontier. | Mark of Austria.♦ Here the frontier, as against Hungary and Croatia, was defended by the marks of _Krain_ or _Carniola_, _Kärnthen_ or _Carinthia_, _Austrian_ mark to the north of them. ♦Little change on this frontier.♦ This frontier has changed least of all. It may, without any great breach of accuracy, be said to have remained the same from the days of the Saxon Emperors till now. The part where it was at all fluctuating was along the Austrian mark, rather than along the two marks to the south of it. ♦Occasional homage of Hungary to the Emperors.♦ The Emperors claimed, and sometimes enforced, a feudal superiority over the Hungarian kings. But this kind of precarious submission does not affect geography. Hungary always remained a separate kingdom; the Imperial supremacy was something purely external, and it was always thrown off on the first opportunity. ♦Frontier towards Denmark.♦ The same may be said of _Denmark_. For a short time a German mark was formed north of the Eider. ♦The Danish Mark, 934-1027. | Boundary of the Eider, 1027-1806.♦ But, when the Danish kingdom had grown into the Northern Empire of Cnut, the German frontier fell back here also, and the _Eider_ remained the boundary of the Empire till its fall. ♦Occasional homage of the Danish Kings.♦ As with Hungary, so with Denmark; more than one Danish king became the man of Cæsar; but here again the precarious acknowledgement of Imperial supremacy had no effect on geography. ♦Slavonic frontier.♦