By the later part of the 18th century much of the fabric of the castle had deteriorated and John Howard, the prison reformer, was particularly critical of the conditions in the prison. Thomas Harrison was commissioned to design a new prison. This was completed in 1792 and praised as one of the best constructed prisons in the country. Harrison then went on to rebuild the medieval Shire Hall in neoclassical style. He also built two new wings, one to act as barracks, the other as an armoury, and designed a massive new entrance to the castle site, styled the Propylaeum. The buildings, which were all in neoclassical style, were built between 1788 and 1822. The architectural historian Nikolaus Pevsner comments that Harrison's work constitutes "one of the most powerful monuments of the Greek Revival in the whole of England".