At the end of the twelfth century a race of ancient Polish princes resided on their paternal inheritance in Silesia; inferior to these were numerous Sclave nobles, and below them again a much oppressed and enslaved people. The country was thinly populated, and poor both in capital and labour. The heights of the Riesenberge and the plains of the Oder were clothed with wood; between them stretched out miles of desolate heath. Herds of wild boars laired in the swamps, bears picked the wild honey from the hollow trunks of the trees, and the elks fed on the branches of the pine; the beaver made its home beside the rivers, the fish eagle hovered about the ponds, and above him soared the noble falcon. The beaver and falcon were more valuable in the eyes of the princes than their serfs. The peasants looked from their miserable huts with horror on the lords of the water and air, for the preservation of which they had to pay exorbitant penalties. What the earth yielded freely they had to collect for their rigorous masters and the Church. They had to pay tribute from the water and the heath of fish and honey, and heavy imposts on their arable land, sheaves of corn, grain and money; and a certain amount of service was required of them. The greater part were serfs; few were free. And not only the peasants, but also the artisans and tradesmen of all kinds lived in every gradation of servitude, ground down by oppression without hope or pleasure in their work. The Sclave cities only differed from the villages in being a larger collection of bare huts, surrounded by a moat and wooden palisades, and usually situated in the vicinity of a nobleman's castle, under whose protection they lived. In peaceable times markets were held in the towns. Even till the end of the twelfth century the merchants often made their payments, as in Poland, with the tails of martins and skins of squirrels instead of money. But the Silesian mines were already being worked; they yielded silver and gold, copper and lead, and mining, which was considered the nobleman's right, was carried on actively. Mints were erected in all the great market towns, and, as in Poland, the coinage was changed three times a year; and the princes derived some of their income from tolls on the market-places, butchers' stalls, and public-houses.