Lincoln castle was built by William the Conqueror in 1068 on a site occupied since Roman times.
To enlarge the site 166 houses were demolished. It is one of only two castles in Britain built with two mottes (Lewes is the other example).
On the larger of the two mottes a 15-sided keep was built and is known as the Lucy Tower after the mother of a 12th century owner, Lucy, Countess of Chester.
A square tower was built on the smaller motte and in the 19th century an observatory was added. The two mottes were enclosed by immense 12th century walls.
The Bishop's palace is a fine example of hall and chamber planning during the 13th century and later.
The castle acted as the city's prison between 1787 and 1878. The coffin-like pews in the chapel were to remind prisoners of their fate and to ensure they could not see each other.