seen. The 43 km section immediately north of Wiseman's Ferry, from Devine's Hill to Mount Manning run through very steep and rugged country and contains particularly fine examples of high walling with massive buttresses, drainage systems and quarries. The walls, up to 13m high, are made of interlocking stone blocks of varying shapes and sizes without mortar to hold them together. Some of the blocks weigh up to 660 kg. Examples of stone work at Clares Bridge and Circuit Flat Bridge are preserved within Dharug and Yengo National Parks. These areas are closed to vehicular access to preserve the remaining convict road works. Other sections of convict work can be seen at Mt McQuoid, Ramseys Leap and the Murrays Run Culvert. Heritage listing The Old Great North Road is a signifier of the outlooks of early colonial society. Its magnificent structures were powerful, tangible symbols of the colony's perceived place and role in the course of empire, unmistakable evidence that the civilised state was being attained and a triumph over a rugged and inhospitable landscape. It is associated with several notable figures in colonial administration, surveying and engineering including Governor Darling, Surveyor General Thomas Mitchell and Percy Simpson, one of Australia's earliest scientific road engineers. The Old Great North Road physically demonstrates the work patterns, skills and organisation of convict work gangs. This evidence is unavailable in documentary sources and has been essential in changing our views of work gangs. It has technological value in that it demonstrates the standards and practice of road engineering in the colony during the "Great Roads" period of the late 1820s and 1830s. Old Great North Road, Between Devine's Hill and Mount Manning was listed on the New South Wales State Heritage Register on 2 April 1999 having satisfied the following criteria. The place is important in demonstrating the course, or pattern, of cultural or natural history in New South Wales. The Great North Road is a signifier of the outlooks of early colonial society. Its magnificent structures were powerful, tangible symbols of the colony's perceived place and role in the course of empire and unmistakable evidence that the civilised state was being attained. It was a triumph over a rugged and inhospitable landscape. It is associated with several notable figures in colonial administration, surveying and engineering. These include, Governor Darling, Surveyor General Thomas Mitchell and Percy Simpson, one of Australia's earliest scientific road