at Papplewick, in Robinson's Mill near Nottingham that a steam engine was successfully used to drive a cotton mill directly. Boulton and Watt's engines enabled mills to be built in urban contexts and transformed the economy of Manchester, whose importance had previously been as a centre of pre-industrial spinning and weaving based on the domestic system. Manchester had no cotton mills until the opening of Arkwright's Shudehill Mill in 1783 and in 1789 Peter Drinkwater opened the Piccadilly Mill – the town's first mill to be directly powered by steam – and by 1800 Manchester had 42 mills, having eclipsed all rival textile centres to become the heart of the cotton manufacturing trade. Water continued to be used to drive rural mills but mills, driven by steam, were built in towns alongside streams or canals to provide water for the engine. Murrays' Mills alongside the Rochdale Canal, in Ancoats were powered by 40 hp Boulton and Watt beam engines. Some were built as room and power mills, which let space to entrepreneurs. The mills, often 'L' or U-shaped, were narrow and multi-storeyed. The engine house, warehousing and the office were inside the mill, although stair towers were external. Windows were square and smaller than in later mills. The walls were of unadorned rough brick. Construction was sometimes to fireproof designs. The mills are distinguished from warehouses in that warehouses had taking-in doors on each storey with an external hoist beam. Only the larger mills have survived. Mills of this period were from 25 to 68 m long and 11.5 m to 14 m wide. They could be eight stories high and had basements and attics. Floor height varied from 3.3 to 2.75 m on the upper stories. Boilers were of the wagon type; chimneys were square or rectangular, attached to the mill, and in some cases part of the stair column. The steam engines were typically low-pressure single-cylinder condensing beam engines. The average power in 1835 was 48 hp. Power was transmitted by a main vertical shaft with bevel gears to the horizontal shafts. The later mills had gas lighting using gas produced on site. The mules with 250–350 spindles were placed transversely to get as much light as possible. Early weaving mills The development of mills to mechanise the weaving process was more gradual partly because of the success of John Kay's 1733 invention of the flying shuttle, which