A traditional unit of distance. Almost every culture has used the human foot as a unit of measurement. The natural foot (pes naturalis in Latin), an ancient unit based on the length of actual feet, is about 25 centimeters (9.8 inches). This unit was replaced in early civilizations of the Middle East by a longer foot, roughly 30 centimeters or the size of the modern unit, because this longer length was conveniently expressed in terms of other natural units: 1 foot = 3 hands = 4 palms = 12 inches (thumb widths) = 16 digits (finger widths). This unit was used in both Greece and Rome; the Greek foot is estimated at 30.8 centimeters (12.1 inches) and the Roman foot at 29.6 centimeters (11.7 inches). In northern Europe, however, there was a competing unit known in Latin as the pes manualis or manual foot. This unit was equal to 2 shaftments, and it was measured "by hand," grasping a rod with both hands, thumbs extended and touching. The manual foot is estimated at 33.3 centimeters (13.1 inches). In England, the Roman foot was replaced after the fall of Rome by the natural foot and the Saxon shaftment (16.5 centimeters). The modern foot (1/3 yard or about 30.5 centimeters) did not appear until after the Norman conquest of 1066. It may be an innovation of Henry I, who reigned from 1100 to 1135. Later in the 1100s a foot of modern length, the "foot of St. Paul's," was inscribed on the base of a column of St. Paul's Church in London, so that everyone could see the length of this new foot. From 1300, at least, to the present day there appears be little or no change in the length of the foot. Late in the nineteenth century, after both Britain and the U.S. signed the Treaty of the Meter, the foot was officially defined in terms of the new metric standards. In the U.S., the Metric Act of 1866 defined the foot to equal exactly 1200/3937 meter, or about 30.480 060 96 centimeters. This unit, still used for geodetic surveying in the United States, is now called the survey foot. In 1959, the U.S. National Bureau of Standards redefined the foot to equal exactly 30.48 centimeters (exactly 0.999 998 survey foot). This definition was also adopted in Britain by the Weights and Measures Act of 1963, so the foot of 30.48 centimeters is now called the international foot. Elsewhere on this page are entries for the Danish fod, Swedish fot, and German fuß (fuss). Other foot units include the French pied, Italian and Spanish pie, and Hungarian láb