YEAR (CONSULAR). — The practice of naming years after the ordinary consuls (not the *suffetti*), whence their designation as “eponymous,” dates from 509 BC and lasted in the West until 534 and in the East until 541. Only from 153 BC did the beginning of the consular year coincide with 10 January; yet the consular year did not always have its normal duration: in certain years it was sometimes only six months or even shorter.
From 535 to 547 AD in the West the formula *p(ost) c(onsultum) Paulini iunioris* I (up to XIII) was used; in the East from 542 to 565 the formula *p. c. Basili iunioris* I (up to XXIV) was employed. In 566, when Justin II appropriated the title of consul for the emperor, the post-consular indication was added after the regnal years, minus one unit: e.g. *Data die X Kal. Augustarum, imperante d. n. Mauricio Tiberio piissimo Aug. an. XIV, p. c. eiusdem d. n. an. XIII, indicione XIV* = 596 (S. Gregori, *Reg.*, VI, 50: Jaffé-Wattenbach, 1434).
Even in Christian monuments and ecclesiastical documents, the consular or post-consular date remained the most common until the 8th century, as is evident, for example, from dated inscriptions spanning the 3rd to the 7th centuries (cf. list in E. Diehl, *Inscriptions lat. christ. veteres*, III, Berlin 1931, pp. 229–63). The aforementioned Byzantine formulary for dating, later adopted in the *Liber Diurnus* (ed. Th. E. von Sickel, Vienna 1889: cf. e.g. form. VII), contributed to the appearance of post-consular years in a number of papal documents until the beginning of the 10th century, attributing them to the Carolingian emperors and, having lost the true understanding of them, equating them with regnal years.
Here is how the date is formulated in the privilege of Paschal I for the Church of Ravenna, dated 11 July 819: *“quinto IIIudorico a Deo coronato magno pacifico imperatore anno sexto, et [post] consulatum eius anno sexto”* (G. Battelli, *Exempla Scripturarum*, fasc. III: *“Acta Pontificum,”* Città del Vaticano 1933, p. 5 and pl. 1).
The last witness to this anomaly is the letter of Pope Sergius III, dated 22 Feb. 904, which records the 4th year and the 4th post-consulate of Louis III (Jaffé-Wattenbach, 3533). The date with the name of the Byzantine emperor and his post-consulate appears for the last time in the privilege of Hadrian I for Farfa, dated 772 (Jaffé-Wattenbach, 2395).