In 1235, the mighty Mongol army launched an invasion of Europe. After the Battle of Legnica, the Mongols carried their devastating raid into Moravia, but they were beaten by the Czech royal army in a battle of Olomouc, where they killed Genghis Khan grandson Baidar and continued into Hungarian lands.
King Přemysl Otakar II earned the nickname "Iron and Golden King" because of his military power and wealth. He acquired Austria, Styria, Carinthia and Carniola, thus spreading the Bohemian territory to the Adriatic Sea. He met his death at the Battle on the Marchfeld in 1278 in a war with his rival, King Rudolph I of Germany. Ottokar's son Wenceslaus II acquired the Polish crown in 1300 for himself and the Hungarian crown for his son. He built a great empire stretching from the Danube river to the Baltic Sea. In 1306, the last king of Přemyslid line was murdered in mysterious circumstances in Olomouc while he was resting. After a series of dynastic wars, the House of Luxembourg gained the Bohemian throne.
The 14th century, particularly the reign of Czech King Charles IV (1316–1378), who became also King of Italy, King of the Romans and Holy Roman Emperor, is considered the Golden Age of Czech history. Of particular significance was the founding of Charles University in Prague in 1348, Charles Bridge, Charles Square and were completed much of the Prague Castle and cathedral of Saint Vitus. He acquired the territory of Brandenburg (until 1415), Lusatia (until 1635), and Silesia (until 1742) under Czech crown. The Black Death, which had raged in Europe from 1347 to 1352, decimated the Kingdom of Bohemia in 1380, killing about 10% of the population.
In the 15th century, the religious and social reformer Jan Hus formed a movement later named after him. Although Hus was named a heretic and burnt in Constance in 1415, his followers seceded from the Catholic Church and in the Hussite Wars (1419–1434) defeated five crusades organized against them by
