As soon, therefore, as there was no superior authority to maintain order and security in the land, a large number of the knights became freebooters, plundering and laying waste whenever opportunity offered, attacking the caravans of travelling merchants, and accumulating the ill-gotten wealth in their strong castles. Many an aristocratic family of the present day owes its inheritance to that age of robbery and murder. The people had few secured rights and no actual freedom in Germany, with the exception of Friesland, some parts of Saxony and the Alpine districts. In this condition of things, the free cities soon found it advisable to assist each other. Bremen, Hamburg and Lübeck first formed a union, chiefly for commercial purposes, in 1241, and this was the foundation of the famous Hanseatic League. Immediately after the death of Konrad IV., Mayence, Speyer, Worms, Strasburg and Basel formed the "Union of Rhenish Cities," for the preservation of peace and the mutual protection of their citizens. Many other cities, and even a number of reigning princes and bishops, soon became members of this league, which for a time exercised considerable power. The principal German cities were then even more important than now; few of them have gained in population or in relative wealth in the course of 600 years. Cologne had then 120,000 inhabitants, Mayence 90,000, Worms 60,000, and Ratisbon on the Danube upwards of 120,000. The cities of the Rhine had agencies in England and other countries, carried on commerce on the high seas, and owned no less than 600 armed vessels, with which they guarded the Rhine from the land-pirates whose castles overlooked its course. During this age of civil and religious despotism, the German cities possessed and preserved the only free institutions to be found. They owed this privilege to the heroic resistance of the republican cities of Italy to the Hohenstaufens, which not only set them an example but fought in their stead. Sure of the loyalty of the German cities, the Emperors were not so jealous of their growth; but some of the rights which they conferred were reluctantly given, and probably in return for men or money during the wars in Italy. The decree which changed a vassal, or dependent, into a free man after a year's residence in a city, helped greatly to build up a strong and intelligent middle-class. The merchants, professional men and higher artisans gradually formed a patrician society, out of which the governing officers were selected, while the mechanics, for greater protection, organized themselves into separate guilds, or orders. Each of the latter was very watchful of the character and reputation of its members, and thus exercised a strong moral influence. The farmers, only, had no such protection: very few of them were not dependent vassals of some nobleman or priest. [Sidenote: 1260.]