3rd century BC

Centuries:	4th century BC - 3rd century BC - 2nd century BC
Decades:	290s BC 280s 270s 260s 250s 240s 230s 220s 210s 200s BC

The 3rd century BC started on January 1, 300 BC and ended on December 31, 201 BC.

Events

The Pyramid of the Moon, one of several monuments built in Teotihuacán

Teotihuacán, Mexico begun
The first two Punic Wars between Carthage and Rome over dominance in western Mediterranean
Rome conquers Spain
Gaulish migration to Macedon, Thrace and Galatia
282-226: Colossus of Rhodes
281 BC Antiochus I Soter, on the assassination of his father Seleucus becomes emperor of the Seleucid empire.
279 BC Singidunum and Taurunum, today's Belgrade and Zemun, founded by Scordisci Celts
275 BC: end of history of Babylon
273 BC to 252 BC Ashoka the Great ruled the Mauryan Empire
261 BC Antiochus II Theos, 2nd son, at the death of his father becomes emperor of the Seleucid empire.
214 BC Qin Shi Huang Qin Dynasty ordered construction of the Great Wall of China.
Indian traders regularly visited Arabia
Scythians occupy Sogdiana, in modern-day Uzbekistan.
Han dynasty was founded (202 BC - 8 AD).
The Pharos of Alexandria is built.
Appearance of the Hopewell culture in Ohio, USA

Bust of Hannibal, the most prominent general of Carthage during the Second Punic War

Appius Claudius Caecus, Aqua Appia, Via Appia, invented letter G
Mencius, Chinese philosopher and sage (371 - 289 BC).
Euclid, geometer (c. 365 - 275 BC).
Ashoka, Mauryan ruler of India 273 BC - 232 BC.
Arcesilaus, founder of new Academy
Archimedes of Syracuse, mathematician, physicist, and engineer (c. 287 - 212 BC).
Manetho, wrote History of Egypt
The Ptolemaic dynasty rules Egypt
- Ptolemy I Soter (305 BC-282 BC) and his wives Eurydice and
- Ptolemy II Philadelphos (284 BC-246 BC) and his wives Arsinoe I and Arsinoe II Philadelphos.
- Ptolemy III Euergetes I (246 BC-222 BC) and his wife Berenice II.
- Ptolemy IV Philopater (222 BC-204 BC) and his wife Arsinoe III.
- Ptolemy V Epiphanes (204 BC-180 BC) and his wife Cleopatra I.
Eratosthenes (c. 276 - 194 BC), Greek mathematician, geographer and astronomer.
Apollonius of Perga, mathematician (c. 262 - 190 BC).
Qin Shi Huang, Chinese Emperor (259 - 210 BC, reigned 246 - 210 BC).
Hannibal, military leader of Carthage (247 - 182 BC).
the "second" Brennus, Gaulish chieftain, invades Macedonia in 279 BC
Xun Zi, founder of Legalism (philosophy)
Zeno of Citium, founder of Stoicism

Eratosthenes accurately calculates diameter of the Earth
Weiqi well-established in China, and may date back to the 2nd millennium BC
Stone of Canopus (for Ptolemy III), No. 1, in Rosetta Stone Series of 3 stones. Implements Leap year in Egypt. Leap year not formally recognized until Caesar in 55 B.C.
293 BC: first Roman Sundial [Pliny (79ce): Natural History 7.213]
Water screw invented by Archimedes
Invention of the musical instrument hydraulis, the precursory to the Pipe organ by Ktesibios, a Greek engineer working in Alexandria.