The Polish state developed from tribal roots in the second half of the century. According to the 12th-century chronicler Gallus Anonymus, the Polans were ruled at this time by the Piast dynasty. In existing sources from the 10th century, Piast ruler Mieszko I was first mentioned by Widukind of Corvey in his Res gestae saxonicae, a chronicle of events in Germany. Widukind reported that Mieszko's forces were twice defeated in 963 by the Veleti tribes acting in cooperation with the Saxon exile Wichmann the Younger. Under Mieszko's rule (ca. 960 to 992), his tribal state accepted Christianity and became the Polish state.