Mapledurham Mill was for many years the only watermill left on the Thames, according to Stan Yorke, author of Windmills and Watermills Explained (Countryside Books, £7.99).

It is a picturesque sight, but Yorke says we must shed romantic images of bygone days and Constable's paintings and remember that the mills were the industry of their day, designed solely to do a job of work. He explains that water and wind continued to be a valuable source of power in the 19th century, well after the arrival of the steam engine, partly because they were cheap and plentiful, and partly because the technology was well understood and the machinery could be started or stopped in minutes.

Mills were often moved or rebuilt as new technologies arrived. At Mapledurham, wedges were used to hold a new cast-iron spoke ring on to the old wooden wheel shaft.

The book includes a list of mills to visit, with contact details - Chinnor windmill being the only other Oxfordshire site listed.