The pertica (from Latin: pertica, measuring rod^[1]) was a pre-metric unit of either length or area, with the values varying by location. For a similar unit in Northern Europe, see perch.

In the Ancient Rome, pertica, also called decempeda,^[2] was a unit of length, usually equal to 10 Roman feet (pedes), or approximately 2.96 meters.^[3] The variants of pertica contained 12^[4] and 15^[5] pedes. Isidore of Seville (per Codex Gudianus) states that sometimes a pertica of 10, 12, 15, or 17 pedes was used by agrimensores (Roman land surveyors) to accommodate the richness of the soil and approximately even the yield per unit area.^[6][7] Kidson^[8] highlights the near-perfect match between the pertica of 17 pedes and the English version of the perch.

The same names, pertica and decempeda, were used for the surveyor's tool, a rod of the corresponding length with subdivision into smaller units, similar to the Ancient Greek kalamos.^[9]

The linear unit in Italy was about 3 meters, area unit contained about 600 square meters. After switching to the metric system, the unit became equal to 1 decare.^[3]

The regional area values significantly varied per province (in square meters):^[10]

• Bergamo 662;
• Como (milanese) 655;
• Cremona 808;
• Pavia 770;
• Piacenza 762;
• Sondrio 688.

• Morwood, James, ed. (2005). The pocket Oxford Latin dictionary: Latin - English. Oxford University Press. ISBN 978-0-19-173958-3.
• Walthew, C. V. (1981). "Possible Standard Units of Measurement in Roman Military Planning". Britannia. 12: 15–35. doi:10.2307/526241. JSTOR 526241.
• Kidson, Peter (1990-01-01). "A Metrological Investigation". Journal of the Warburg and Courtauld Institutes. 53 (1): 71–97. doi:10.2307/751340. ISSN 0075-4390. JSTOR 751340.
• Duncan-Jones, R. P. (1980). "Length-Units in Roman Town Planning: The Pes Monetalis and the Pes Drusianus". Britannia. 11: 127–133. doi:10.2307/525675. JSTOR 525675.
• Senseney, John R. (2013-10-28). "Plans, Measurement Systems, and Surveying: The Roman Technology of Pre-Building". A Companion to Roman Architecture. Wiley. pp. 140–156. doi:10.1002/9781118325117.ch8. ISBN 978-1-4051-9964-3.

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