|Ab urbe condita||1256|
|Balinese saka calendar||424–425|
|Chinese calendar||壬午年 (Water Horse)|
3199 or 3139
— to —
癸未年 (Water Goat)
3200 or 3140
|- Vikram Samvat||559–560|
|- Shaka Samvat||424–425|
|- Kali Yuga||3603–3604|
|Iranian calendar||119 BP – 118 BP|
|Islamic calendar||123 BH – 122 BH|
|Minguo calendar||1409 before ROC|
|Seleucid era||814/815 AG|
|Thai solar calendar||1045–1046|
629 or 248 or −524
— to —
630 or 249 or −523
Year 503 (DIII) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Volusianus and Dixicrates (or, less frequently, year 1256 Ab urbe condita). The denomination 503 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- War with Sassanid Persia: Emperor Anastasius I sends a Byzantine army (52,000 men) to Armenia, but is defeated. The Romans attempt an unsuccessful siege of the Persian-held city Amida, on the Tigris. King Kavadh I invades Osroene, and lays siege to the city of Edessa (Northern Mesopotamia).
- May – Areobindus, Byzantine general (magister militum), is stationed as commander at Dara, with an army of 12,000 men to keep watch at the Persian stronghold of Nisibis (modern Turkey).
- Mundhir III, king of the Lakhmids (Arab Christians), raids Palaestina Salutaris and Arabia Petraea. He captures a large number of Romans.
- King Ernakh, third son of Attila the Hun, dies after a 34-year reign. He is succeeded by his two sons (Utigur and Kutrigur), who share the power with the unified Bulgars.
- October 17 – Lý Nam Đế, first emperor of Vietnam (d. 548)
- December 2 – Xiao Gang, later Emperor Jianwen of Liang, emperor of the Chinese Liang dynasty (killed 551)
- Chen Baxian, later Emperor Wu of Chen, first emperor of the Chinese Chen dynasty (d. 559)
- Greatrex & Lieu 2002, pp. 69–71
- John Binns, Ascetics and ambassadors of Christ: the monasteries of Palestine, 314-631. p.113; Frank R. Trombley, J. W. Watt, The chronicle of pseudo-Joshua the Stylite (the margin) p.108; Cyril of Scythopolis, Life of John the Hesychast, p.211. 15-20
- Priscus. Excerpta de legationibus. Ed. S. de Boor. Berolini, 1903, p. 586
- Greatrex, Geoffrey; Lieu, Samuel N. C. (2002). The Roman Eastern Frontier and the Persian Wars (Part II, 363–630 AD). New York, New York and London, United Kingdom: Routledge (Taylor & Francis). ISBN 0-415-14687-9.CS1 maint: ref=harv (link)