In 671, at the Battle of Two Rivers, Ecgfrith put down an opportunistic rebellion by the Picts, which resulted in the Northumbrians taking control of the land between the Firth of Forth and the Tweed for the next fourteen years. Around the same time, Æthelthryth wished to leave Ecgfrith to become a nun. Eventually, in about 672, Æthelthryth persuaded Ecgfrith to allow her to become a nun, and she entered the monastery of the Abbess Æbbe, who was aunt to King Ecgfrith, at Coldingham. A year later Æthelthryth became founding abbess of Ely. Her taking the veil may have led to a long quarrel with Wilfrid, Archbishop of York, which ended with Wilfrid's expulsion from his Episcopal see.