A Dictionary of Greek and Roman Antiquities (1890)
William Smith, LLD, William Wayte, G. E. Marindin, Ed.

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LIBELLA

LIBELLA

1. The diminutive form of libra, a Roman pound, and naturally applied not to the heavy pound of copper, but its equivalent in silver. Varro writes as follows (L. L. 5.174) of the libella: “Nummi denarii decuma libella, quod libram pondo as valebat, et erat ex argento parva.” This phrase has been much discussed, and has misled many metrologists, but the latest researches (Hultsch, Metrologie, ed. 2, p. 275) seem to show that Varro's words contain two errors and one truth. He is wrong in supposing that the denarius was ever equal in value to ten heavy or libral asses; in fact it was equivalent to four (As, p. 205): and he is wrong in supposing that the libella was ever issued as an actual coin; it was in fact a mere money of account, like the guinea among ourselves. But he is probably right in his assertion that originally the libella was the tenth of a denarius, and so equal to seven grains of silver, or one as of the triental reduction [As, Vol. I., p. 205]. Later it was reckoned as the tenth of the sestertius, and so as equivalent only to 175 grains of silver. The half of the libella was the sembella (Varro, 5.174), and its quarter the teruncius. The relation (one-tenth), of the libella to the sestertius or denarius gave rise to the phrase “heres ex libella.” (Cic. Att. 7.2, 3), applied to those who inherited the tenth of an estate; while he who inherited the fortieth part was called “heres ex teruncio” (ib.). [P.G]

2. (Also, but less frequently libra.) A carpenter's level, called by the Greeks διαβήτης, and also in poets (from the pendant tongue) σταφυλή (Horn. II. 2.765,

Libella, a carpenter's level. (From a grave-stone, Gruter, p. 644, 1.)

where Schol. σταφυλὴ γὰρ ὁ τεκτονικὸς διαβήτης): in Col. 3.13, 12, libella fabrilis,--cf. Plin. Nat. 36.172; Vitr. 3.5, 2: in Lucret. 4.515 (where other instruments also are mentioned), “libella aliqua si ex parti claudicat hilum,” the idea is clearly of the legs not being set truly. In Caesar (B.C. 3.40) the form libra is used, which seems to be the regular form when it is applied to water-level, so that infra libram maris means “below the sea-level.” (Blümner, Technologie, &c., ii. p. 236.)

[G.E.M]