William de Roumare, Earl of Lincoln (born circa 1096) built Old Bolingbroke Castle in the 12th century, a motte and bailey castle, with a wet ditch. In the early 13th century, a new castle was constructed at the present site by Ranulph de Blondeville, 4th Earl of Chester. Later John of Gaunt, the son of Edward III, acquired the castle; and in 1367 it became the birthplace of John's son Henry, known as Henry Bolingbroke, who became King Henry IV of England. The castle underwent a Civil War siege in 1643, as the Royalists used it to garrison troops prior to the Battle of Winceby (11 October 1643). The last remaining structure fell down in 1815. The site eventually became a grassy hillock, which archeologists excavated in the 1970s.