The war intensified in 1757 with an Austrian invasion of Prussia. Fredrick countered this army by organizing his own, 100,000 strong, and invading the Austrian Bohemia in four columns. The Austrians abandoned their invasion plans in favor of defense, organizing their army into a long brittle column along the border. After a fairly easy breakthrough, the Austrians fell into a disorderly retreat, and Fredrick began to advance on the Austrian capital of Prague, while also diverting forces to harass the French. Fredrick defeated the main Austrian army outside Prague in a bloody and close fought battle and laid siege to the Austrian capital. However, in June, an equally bloody battle at Kolín forced Fredrick to withdraw back north. While his southern operations were going sour, a French army invaded Germany from the west, defeating Prussia's British and Hanoverian allies along the way.