Occupatio
Occupatio is the advisedly taking possession of a thing which belongs to no one (res nullius), with the intention of appropriating it: the property in it is thereby ipso facto vested in him who takes possession (Cic. de Off. 1.7, 21): quod nullius est, id ratione naturali occupanti conceditur
(Dig. 41, 1, 3, pr.). Hence (following Gaius, 2.66, and also in the passage just cited) Justinian enumerates occupatio in his Institutes as one of the ad quisitiones naturales, or modes of acquiring property recognised practically among all peoples, as being based on the jus gentium or naturale. Among the things of which one can become owner in this fashion are wild animals, birds, bees, and fishes (Inst. 2.1, 12-16), enemies' property on Roman soil (ib. 17), stones and pebbles found on the sea-shore (ib. 18), islands which rise in the sea (ib. 22), treasure trove (ib. 39), and res derelictae, property abandoned by its former owner (ib. 47).
From William Smith (ed.), Dictionary of Greek and Roman Antiquities. Text provided under a CC BY-SA license by Perseus Digital Library, http://www.perseus.tufts.edu, with funding from the National Endowment for the Humanities and Tufts University. Data accessed from https://github.com/PerseusDL/canonical-pdlrefwk/ on 17 October 2026.