Despite the aid of Bohemian and Lutici allies, the Imperial attack was ultimately unsuccessful, according to medieval chronicler Thietmar of Merseburg due to the arrival of reinforcements which managed to break into the city and the illness among the German forces.

The former Bohemian fortress of Niemcza, located north of the Sudetes range on an important trade route from Prague to Wrocław, had been conquered by the late Polish duke Mieszko I during his campaigns into Silesia about 990.

In the ensuing power struggle of the royal election for the leadership of the Holy Roman Empire, Bolesław supported his relative (possibly half-brother) Margrave Eckard of Meissen against Henry II.

The German king realised that the Polish advance could pose a serious threat to his rule; he concluded an alliance with the pagan Lutici and campaigned Bohemia and the Milceni lands.

Under constant attacks by Bolesław's forces, Henry II turned southeastwards and passed Głogów to encounter the Polish army at the large fortress of Niemcza in August 1017.

While Bolesław's men entrenched themselves, the emperor laid siege to the Niemcza fortifications but was unable to supply the besieging force with food for a long time.

At the 1054 Diet of Quedlinburg, Emperor Henry III officially ceded the Silesian territories to Polish rule against the payment of an annual tribute to the Bohemian dukes.