William the Conqueror built the castle. The text dates it to the late 11th century and says the new fortification was completed in 1068. A wooden keep was probably built first and later replaced in stone. The outer walls date from before 1115. It has two mottes, one of only two such castles in England, and the curtain wall reuses sections of Roman wall.
The Lucy Tower was built after the First Battle of Lincoln in 1141, and barbicans were added after 1215. The gaol opened in 1787 and the prison was extended in 1847. Public hangings took place on the mural tower until 1868.
The castle displays one of four surviving 1215 Magna Carta exemplars, in an exhibition center from the 2012 to 2015 renovation. It is Grade I listed, and the council owns it. The Crown Court still sits on the site.

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