Cotton is most easily worked in a place with high humidity. Manchester was ideally placed in this respect, and it was directly related to the growth of the city. The earliest cotton mills were in Ancoats, and the need for warehouses to store their products led to specially designed buildings being built nearer the centre of the city. By the middle of the nineteenth century, Manchester had become the largest textile centre in the world. As a result, the need for warehousing grew and it is these buildings, larger than before and built with considerable architectural characteristics that form the Whitworth Street/Princess Street conservation area.
The distinctive architecture which arose was both functional and expressive of the wealth of the owners. The front of the warehouses facing the main street was often used for offices whilst the rear of the building was used for storage space and for the inspection of the cotton goods in natural light. This led to six- or seven-storey buildings with opulent and deeply modelled front facades in brick and/or terracotta, whilst the rear was almost entirely glazed either in a vertical plane or a stepped configuration. The building style reached its zenith in the early years of the twentieth century, and culminated in the grand Edwardian commercial architecture of Whitworth Street.
The architecture of textile marketing remains largely intact in the area around Princess Street and Whitworth Street, though its association with the industry has decreased since the cotton slumps of the 1920s.
At the industry's height, vast quantities of cotton were being handled, in all its stages from the raw state to the finished product, and transport was of paramount importance. The Rochdale Canal had been planned in 1765 by James Brindley, but was not completed until 1804 when it joined the Ashton Canal to the north of the city centre. In 1805, John Rennie engineered its connection to the 1760 built Bridgewater Canal, to the south of the city centre. From then on it was possible to transport coal cheaply along the canal to power mill machinery, a vital influence in the sudden growth of the cotton industry. Once a major commercial thoroughfare, the canal is now used only by leisure traffic, although its presence is an important ingredient in the regeneration efforts in this part of the city.