The influence of geographical environment on man is also noted by some of the writers of our period. Otto of Freising explains[1059] that the Lombards on entering Italy gave up their wild customs and adopted Italian ways, partly because they married native women but partly as a result of the nature of country and climate. Giraldus tells how the plains of southern Wales are far more pleasant to live in than those of the north.[1060] The latter region, on the other hand, has not only better natural defenses but a richer soil and is more fertile in producing men of strength and power. Gunther in the _Ligurinus_[1061] enlarged on Ragewin’s simple description (in his continuation of Otto of Freising’s _Gesta Friderici_) of the wild ferocity of the natives of Poland by saying that their fierceness and savagery is due partly to the nature of the soil and partly to the influence of their neighbors. _Topography As a Natural Defense_ In the same connection these authors try to show that topography may often serve as a natural defense against hostile invaders. Giraldus speaks of Wales[1062] as a country easily defensible because of the depth of its valleys and the immensity of its woods, waters, and swamps. The remnants of the ancient Britons who were driven here were able to hold out and preserve their independence against both Angles and Normans. On the other hand, those who were driven into the southern promontory (Cornwall), where the land was not by nature so easy to defend, yielded to the conqueror. In another connection[1063] Giraldus speaks of the difficulties any one would encounter in trying to conquer such a rough country as Wales and one so well fortified by nature. Gervase of Tilbury also testifies to the strong natural defenses of Wales,[1064] specifying how the Welsh, when enemies appear, take to the bog lands on the mountains, which they can easily cross through an agility resulting from long familiarity. Here they either escape from their enemies or lie in wait to inflict grave harm on them. Giraldus[1065] tells that the islands in the lakes of Ireland were used for refuges as well as for dwelling places by the lords of the surrounding districts; and Ragewin[1066] speaks of the natural defenses of Genoa, hemmed in on one side by mountains and on the other by the sea. _Theory of the Westward Flow of Civilization_