We find these refugee folk living in pile villages built over the water, in deserts, in swamps, mangrove thickets, very high mountains, marshy deltas, and remote or barren islands, all which can be classified as regions of retreat.

Fugitives try to place between themselves and their pursuers a barrier of sea or desert or mountains, and in doing this have themselves surmounted some of the greatest obstacles to the spread of the human race.
Districts of refuge located centrally to several natural regions of migration receive immigrants from many sides, and are therefore often characterized by a bizarre grouping of populations.

The cluster of marshy islands at the head of the Adriatic received fugitives from a long semi-circle of north Italian cities during the barbarian invasions.
Each refugee colony occupied a separate island, and finally all coalesced to form the city of Venice.

Central mountain districts like the Alps and Caucasus contain "the sweepings of the plains." The Caucasus particularly, on the border between Europe and Asia, contains every physical type and representative of every linguistic family of Eurasia, except pure Aryan.

Nowhere else in the world probably is there such a heterogeneous lot of peoples, languages and religions.