Not only heroes (and their horses) but also forces of nature—such as rivers, as here—can have menos. In the comments so far, menos has been consistently translated as ‘mental power’, not just ‘power’, and this translation can apply even in the present context, I.12.018. Forces of nature can have a mind of their own, as it were, because they are connected to the mental power of divinities who control the cosmos and to whom humans using their own mental power can pray for the activation of such control. Besides rivers, as here, other natural forces that have menos include the sun (I.23.190), fire (I.06.182, I.17.565), and winds (O.19.440). Like heroes, cosmic forces have to be reminded of their menos, and this is precisely what gets done by worshippers who use their own mental power in praying to divinities controlling such cosmic forces, as we see for example in Indic traditions centering on the word mánas-, which I likewise translate as ‘mental power’ and which is actually a cognate of Greek menos.