[258] ὕδατι ῥόον ἡγεμονεύηι, on the analogy of “ὁδὸν ἡγεμονεύειν τινί”, e.g. Od. 24.225 (the same construction is found with “ἡγεῖσθαι” also, see Lex.). Good authorities have “ὕδατος”, but the gen. cannot be used with the acc.; “ἡγεμονεύειν τινός” is another thing.