Summary: According to "Gesta episcoporum Cameracensium", emperor Otto II invaded Slavs towards the end of 979. Although it is not certain, there are some hints showing Mieszko I and his state as an object of aggression by German troops. Probably the emperor's aim was to force the Polish prince, who had supported the Bavarian Prince Henry the Wrangler aspiring to gain power from the beginning of 70s at the expense of Otto II, to obey him. There are numerous difficulties to determine the military actions at the time. However, a short story by Thietmar, a chronicler, turns useful by mentioning a war in which the Piasts managed to capture a number of prisoners. The conflict mentioned by the chronicler apparently reminiscences the war reported by the author of "Gesta episcoporum Cameracensium". Therefore it may be presumed that the German-Polish war in 979 was victorious for Poland. Defeating Germans by Mieszko was probably through irregular actions. Another cause of defeat over German knights was probably the weather which deterred from military actions on a larger scale. Mieszko I supposedly led the knights skillfully during the war with the empire. He did not let Otto I enter the centre of his land which may be concluded on the basis of the provisions of the peace settlement made later between the Piasts and the Liudolfings. It was the German side that wanted a quick settlement of bilateral relations and they even brought a nun Oda (daughter of Dietrich, a Saxon Margrave) from a monastery to offer as a wife to Mieszko. This way the duke of the Piast dynasty became a member of the imperial aristocracy and could establish contacts with Saxon princes without any problems.