Manchester is credited as the world's first industrialised city and for the subsequent central role it played during the Industrial Revolution. It was the dominant international centre of textile manufacture and cotton spinning. During the 19th century it was nicknamed Cottonopolis, denoting that the area was a metropolis of cotton mills. Manchester City Centre is now on a "tentative list" of UNESCO World Heritage Sites, mainly due to its network of canals and mills, which facilitated its development during the 19th century.