PROPIOS, or PROPRIOS, Span. law. Certain portions of ground laid off and reserved when a town was founded in Spanish America, as the unalienable property of the town, for the purpose of erecting public buildings, markets, &c., or to be used in any other way, under the direction of the municipality, for the advancement of the revenues, or the prosperity of the place. 12 Peters' R. 442, note.