Walloons belonged to the first ambassadors of western culture in Silesia, working in various fields and places in the middle and late 12th century. Noticeable were weavers in Wrocław and Oława, peasants near Wrocław, Oława and Namysłów and Augustinian monks from Arrouaisse in Sobótka. The German Ostsiedlung was started at the same time by the ruling Piasts in order to develop their realms and to increase their power. Silesia then was sparsely populated with approximately 150,000 people. Settlements consisted of small hamlets, each inhabited by only a few peasants. Castellanies with small suburbias around them were centers of administration, commerce and crafts. In 1155 probably 20 castellanies existed across Silesia. Some marketplaces existed without an accompanying castle, like Środa Śląska or Sobótka. These settlements were already noticeable towns in an economic sense, while most of the larger ones were a ruler's residence. Contemporary sources record 8 markets in Silesia, but the real number was probably much higher. The castellanies with their fortified churches were the center of the church organization, while the network of churches was very coarsely meshed and multiple villages belonged to single parishes. The dominions were protected by the so-called "Preseka" (, ), a wide, fortified strip of woodland which had to be maintained by the Polish peasants.