Weights and measures in Roman Britain

Trade, commerce and construction work depended on the use of standard measures. The weight of gold and silver coinage was applied strictly in towns and forts; farm produce and food were sold according to a standardised system of weights and measures. Although, as evidence has revealed in Britain, provinces across the Empire often operated a dual system as Roman standards took over those already in use by the native population.

The standard of length was the Roman foot, which measured 296 millimetres. Folding foot rules of bronze were further subdivided into fourths (palmi), twelfths, (unciae), and sixteenths, (digiti). The standard Roman units of capacity for liquid and dry commodities were the modius (about 8.6 litres) and the sextarius, one sixteenth of a modius (about half a litre). The Roman standard of weight was the libra or pound (about 327 grammes), which was divided into 12 unicae or ounces (about 27 grammes).

The two main types of scales were the simple balance (libra) and the more common asymmetrical balance or steelyard (statera). The libra was used principally for weighing out small amounts. The steelyard, a portable and versatile device, could weigh a wider range of produce and was particularly useful for street sellers and shopkeepers. It is still used in some parts of the world.

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