|Millennium:||1st millennium BC|
|203 BC by topic|
|Gregorian calendar||203 BC|
|Ab urbe condita||551|
|Ancient Egypt era||XXXIII dynasty, 121|
|- Pharaoh||Ptolemy V Epiphanes, 1|
|Ancient Greek era||144th Olympiad, year 2|
|Balinese saka calendar||N/A|
|Chinese calendar||丁酉年 (Fire Rooster)|
2494 or 2434
— to —
戊戌年 (Earth Dog)
2495 or 2435
|Coptic calendar||−486 – −485|
|Ethiopian calendar||−210 – −209|
|- Vikram Samvat||−146 – −145|
|- Shaka Samvat||N/A|
|- Kali Yuga||2898–2899|
|Iranian calendar||824 BP – 823 BP|
|Islamic calendar||849 BH – 848 BH|
|Minguo calendar||2114 before ROC|
|Seleucid era||109/110 AG|
|Thai solar calendar||340–341|
−76 or −457 or −1229
— to —
−75 or −456 or −1228
Year 203 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Caepio and Geminus (or, less frequently, year 551 Ab urbe condita). The denomination 203 BC 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.
- The Roman general, Publius Cornelius Scipio, while undertaking peace negotiations with the Carthaginians at Utica, makes a surprise attack on the Carthaginian camp and destroys it. Then, sweeping down on the forces that the Carthaginians and their allies, the Numidians, are trying to muster on the Great Plains near the upper Bagradas River (in modern Tunisia), he smashes that army in the Battle of the Great Plains. The Numidian king, Syphax, and the Carthaginian leader, Hasdrubal Gisco, manage to escape separately.
- The Roman general, Gaius Laelius, and Rome's Numidian ally, Masinissa, follow Syphax towards Cirta, the Numidian capital. In the pursuit, Syphax is captured after his badly wounded horse throws him off. He is delivered to Scipio and is made a prisoner of the Romans, dying in the Italian town of Alba Fucens later in the year.
- Masinissa becomes king of both the Massyli and the Massaesyli tribes in Numidia and remains a loyal ally to the Romans.
- Hasdrubal Gisco persuades the Carthaginians to raise a new army and to send for Hannibal to return home from Italy. Hannibal finally leaves Italy and returns to Carthage.
- The Carthaginian general, Mago Barca, is defeated and wounded by the Romans in a battle in Cisalpine Gaul. He dies of his wounds on the return voyage to Carthage.
- A preliminary armistice between Carthage and Rome is declared and the Carthaginian armies accept Scipio's severe terms. However, on his return to Carthage, Hannibal concentrates the remnants of the Carthaginian forces at Hadrumetum (modern Sousse, Tunisia) and prepares them for battle.
- Polybius, Greek historian, famous for his book called "The Histories" or "The Rise of the Roman Empire", covering in detail the period between 220 and 146 BC (d. 120 BC)
- Mago Barca, Carthaginian general during the Second Punic War against Rome who has accompanied his brother Hannibal on the invasion of Italy (b. 243 BC)
- Quintus Fabius Maximus Verrucosus, Roman general and statesman whose cautious delaying tactics (which have led to his surname Cunctator, meaning "delayer") during the early stages of the Second Punic War has given Rome time to recover its strength and take the offensive against the invading Carthaginian army of Hannibal (b. c. 275 BC)
- Syphax, Numidian king allied with the Carthaginians during the Second Punic War against Rome