In 1139, Matilda crossed to England to take the kingdom by force, supported by her half-brother Robert of Gloucester and her uncle King David I of Scotland, while her husband, Geoffrey, focused on conquering Normandy. Matilda's forces captured Stephen at the Battle of Lincoln in 1141, but the Empress' attempt to be crowned at Westminster collapsed in the face of bitter opposition from the London crowds. As a result of this retreat, Matilda was never formally declared Queen of England, and was instead titled "Lady of the English" (). Robert was captured following the Rout of Winchester in 1141, and Matilda agreed to exchange him for Stephen. Matilda became trapped in Oxford Castle by Stephen's forces that winter, and to avoid capture was forced to escape at night across the frozen River Isis to Abingdon, reputedly wearing white as camouflage in the snow. The war degenerated into a stalemate, with Matilda controlling much of the south-west of England, and Stephen the south-east and the Midlands. Large parts of the rest of the country were in the hands of local, independent barons.