With a Tower mill, the main structure is built of brick or stone and so cannot be
rotated. The sails are mounted in a separate wooden cap which is arranged so
that it can turn on the top of the tower. This cap is rotated either by hand,
usually using gearing worked by chain from below or by a drive from a fantail.
The ones pictured here are from Thaxted (c.1804), Rayleigh (built in 1809 and
the tallest in the county) and Stansted Mountfitchet (1787).