Weights & Measures

Since the Roman system of weights and measures is fairly complex and of limited interest to most readers of Latin literature, and since only a few technical treatises (e.g. works on agriculture [Cato, Varro, Columella], or architecture [Vitruvius], or astronomy [Manilius] or medicine [Celsus]) require more than the most basic knowledge of it, only minimal and miscellaneous information is provided here. (Most people nowadays have only a general notion of measurement. How much wood is in a cord, wool in a skein, oil in a barrel, pickled pepper(s) in a peck, whiskey in a fifth? (A fifth, a measurement for liquor mostly in the USA, is a fifth of a gallon (= four-fifths of a quart[er of a gallon].) Might a Shetland pony be 18 hands, and how is the measurement taken? How much bigger is a hectare than an acre? Is 10 mph quicker than 10 knots, and why are knots so called? Which weighs more, a ton or a tonne, 10 stone of feathers or 100 lbs of gold?)

amphora, -ae fem. 1 amphora. An amphora contained a Roman cubic foot, equivalent to about 26 litres, and was the basis of liquid measurement. It comprised 48 sextāriī (-ōrum masc. 2) or 8 congiī (-ōrum masc. 2). A standard model, the amphora Capitōlīna, was kept in the temple of Jupiter Optimus Maximus on the Capitol. Like some other Roman terms for weights and measures, amphora is Greek, just as we use the avoirdupois weight system and the Troy system may be named after Troyes in France. A platinum-iridium cylinder is kept at Sèvres as the international prototype for the kilogram, the basic unit of mass.

iūgerum, -ī neut. 2. The iūgerum was the basis of square measurement. It is often loosely translated as “acre”, but it contained 28,800 Roman square feet, and is therefore equivalent to about a quarter of a hectare or three fifths of an acre. iūgerum is cognate with “yoke” (which is the same word as iugum, -ī neut. 2). It was explained in antiquity as the amount of land which a pair of oxen could plough in a day; cf. “furlong” = “as long as a furrow”. At one time, a hērēdium (-, neut. 2), the amount of land that a peasant might normally inherit, was reckoned at two iūgera. “Acre” and ager, agrī masc. 2 “field” are cognate, but the earlier, Indo-European, sense was, conversely, “wild place”. The Romans thought ager was derived from agere, in the sense “do”; i.e. a place of (hard) work.

libra, -ae fem. 1. The libra was the basis for measuring weight. It approximated to the modern pound, but its value varied significantly not only over time but in different regions of the empire. libra give us our modern abbreviation for the pound, lb. By extension, libra also meant “pair of scales”. After the sacking of Rome c. 387 BC, the Gauls agreed to leave on payment of 1,000 pounds of gold. While the gold was being weighed, the Romans complained that the scales were incorrect. The Gallic leader, Brennus, threw his sword on the scales, crying vae victīs (“Woe to the conquered!”). (Brennus may not have been his actual name, but rather a Celtic word for “king”, just as the name of the Illyrian queen Teuta who opposed the Romans in the next century may be simply a version of an Illyrian word for “queen”.)

modius, - masc. 2, equivalent to about 8.75 litres, was the basis of dry measurement. It consisted of 16 sextāriī (-ōrum masc. 2).

passus, -ūs masc. 4 “pace”. The Romans not generally being very tall, their mile (mille passūs) was 1,618 yards long, as opposed to the present 1,760 yards. Similarly, pes, pedis masc. 3 “foot” was about 11 and a half inches. The milliārium aureum “Golden Milestone” was a column covered in gilt bronze, erected in the forum Romanum by Augustus in 20 BC, as the point from which the great roads led out of the city. The Zero Milestone, a granite block, was dedicated in Washington DC in 1923 on the model of the milliārium aureum.

uncia, -ae fem. 1. A unit of weight and measurement. An uncia is the twelfth part of both a pēs (foot) and a libra (pound), and the source of both “inch” and “ounce”. The uncial script is common in early manuscripts. The phrase unciālēs litteræ is first attested in St. Jerome, and “is commonly explained as meaning ‘letters of an inch long’; his use of the word is accompanied by the phrase ut vulgō aiunt [as is commonly said], and the literal sense was perhaps not seriously intended. The emendations initiālēs ‘initial’ and uncinālēs ‘hooked, bent’, have been suggested” (OED s.v. uncial).