Complex sentence: Wallace rose to prominence in May 1297, when he killed Sir William Haselrig, the English sheriff of Lanark, and members of his garrison at Lanark, with the aid of Sir John Graham.
Split into simpler sentences: Wallace rose to prominence in May 1297, when he killed Sir William Haselrig, the English sheriff of Lanark. Wallace killed the sheriff and members of his garrison at Lanark, with the aid of Sir John Graham.