During its history Oława was destroyed completely three times. In 1241 it was destroyed during the First Mongol invasion of Poland, in 1448 by the Hussites, and again in 1634 during the Thirty Years' War. After the Polish King Casimir III had renounced his rights on Silesia with the contract of Trenčín in 1335, Silesia became until 1806 a part of the Holy Roman Empire as a Bohemian fief, although the town remained under the rule of the Polish Piast dynasty as part of the Duchy of Legnica until 1675. In 1526, when the Habsburgs gained the Bohemian crown, Silesia came under Austrian suzerainty. In 1527 with the Reformation High German language came in use and with it the first usage of the version of the town's name "Ohlau" is reported. Following the death of the last Silesian Piast duke George IV William of Legnica in 1675, Oława ceased to be a residence town. In spite of Habsburg political influence, in the 17th century, the town was still part of the territory dominated by the Polish language. Oława found itself again under Polish rule, when Polish prince James Louis Sobieski, son of King John III Sobieski, became duke of Oława in years 1691–1737. Together with most of Silesia, the town became part of the Kingdom of Prussia in 1742.