Altum gurgitem Tigris premens: what is Tigris doing? Gronovius has no remark to the point. The context however points the way to interpretation. For in the list of four rivers, two others are given some word or phrase to characterize them: Hydaspes is gemmifer and Baetis is said to give his name to nearby lands. Thus altum gurgitem premens should refer to some characteristic act or condition of Tigris, not to a unique or casual occurrence. H. M. Kingery (1908, reprinted 1966) cannot be right in saying that ‘the Tigris, noted for its swift current, is pictured here as checking its deep torrent, so as to water the plants that grow in or near its bed’;