Writers have expressed the view that man's interest in projects for establishing perpetual peace is as old as man's participation in warfare. We cannot be certain that Europe can be considered the cradle of such projects for peace, although the Greek city states certainly elaborated a complex system of treaty relationships between themselves to that end. Europe was not to see a like network of sophisticated treaty relationships until the 19th century. Supporting these elaborate treaty networks was the fact that the Greeks enjoyed a common religious-legal and linguistic substratum which tended to mitigate the harshness of the intense intercity rivalries and enmities. The Greeks, as in so many other excursions in thought, were the architects of the modern array of different kinds of political treaties, e.g., of alliance, confederation, federation and, from the 4th century B.C., peace treaties of unlimited duration. In particular, religious leagues were established for the common defence of a shared and sacred shrine. Such were the Amphictyonys of the 5th century B.C. The religious bond between the cities parties to such compacts extended into the political sphere so that the city states bound thereby became confederated by the terms of the amphictyony, as was the case of the confederate association for the protection of the great shrine at Delphi.