AES UXORIUM, a tax paid by men who reached old age without having married. It was first imposed by the censors, M. Furius Camillus and M. Postumius, in B.C. 403, but we do not know whether it continued to be levied afterwards (Festus, s.v.; Val. Max. ii.9 §1; Plut. Camill. 2). [Julia et Papia Poppaea.]

William Smith, A Dictionary of Greek and Roman Antiquities (London: John Murray, 1875), p 26-27.