<Tr> <Th> Size </Th> <Td> 21,196 km (13,171 mi) </Td> </Tr> <Tr> <Th_colspan="2"> UNESCO World Heritage Site </Th> </Tr> <Tr> <Th> Criteria </Th> <Td> Cultural: (i), (ii), (iii), (iv), (vi) </Td> </Tr> <Tr> <Th> Reference </Th> <Td> 438 </Td> </Tr>

When did they finish the great wall of china