The 3rd century BC started the first day of 300 BC and ended the last day of 201 BC. It is considered part of the Classical era, epoch, or historical period.
In the Mediterranean the first few decades of this century were characterized by a balance of power between the Greek Hellenistic kingdoms in the east, and the great mercantile power of Carthage in the west. This balance was shattered when conflict arose between Carthage and the Roman Republic. In the following decades, the Carthaginian Republic was first humbled and then destroyed by the Romans in the first and second Punic wars. Following the Second Punic War, Rome became the most important power in the western Mediterranean.
In India, Ashoka ruled the Maurya Empire. The Pandya, Chola and Chera dynasties of the classical age flourished in the ancient Tamil country.
The Warring States period in China drew to a close, with Qin Shi Huang conquering other nation-states and establishing the short-lived Qin dynasty, the first empire of China, which was followed in the same century by the long-lasting Han dynasty. The Protohistoric Period began in the Korean peninsula. The Xiongnu were at the height of their power in Mongolia.
299 BC: The Samnites, seizing their chance when Rome is engaged on the Lombard plain, start the Third Samnite War with a collection of mercenaries from Gaul and Sabine and Etruscan allies to help them
298 BC: The Samnites defeat the Romans under Lucius Cornelius Scipio Barbatus in the Battle of Camerinum, first battle of the Third Samnite War
293 BC: The Chinese State of Qin reduced the threat of the State of Wei and the State of Han with the Qin victory in the Battle of Yique
Roman armies penetrate into the heart of the Samnite territory and then capture the Samnite cities of Taurasia, Bovianum Vetus and Aufidena
Agathocles, king of Syracuse, Sicily, assists the Italian Greeks against the Bruttians.
Ptolemy finally brings the rebellious region of Cyrene under his control. He places the region under the rule of his stepson Magas.
Bindusara succeeds his father Chandragupta Maurya as emperor of the Mauryan Empire
Theater, Epidauros, is built with later additions
281 BC: Antiochus I Soter, on the assassination of his father Seleucus becomes emperor of the Seleucid empire
280 BC: King Pyrrhus of Epirus invades Italy in an attempt to subjugate the Romans and bring Italy under a new empire ruled by himself
280 BC: Construction of the Colossus of Rhodes is completed
279 BC: Singidunum and Taurunum, today's Belgrade and Zemun, are founded by Scordisci Celts.
After failing to decisively defeat the Romans, Pyrrhus of Epirus withdraws from Italy.
Gallic migration to Macedon, Thrace and Galatia.
273 BC – 232 BC: Ashoka ruled the Maurya Empire.
265 BC: Kalinga War takes place between Ashoka and the kingdom of Kalinga.
264 BC: First Punic War breaks out between the Carthaginian Empire and the Roman Republic.
261 BC: Antiochus II Theos, 2nd son, at the death of his father becomes emperor of the Seleucid empire.
260 BC: Battle of Changping between the State of Qin and the State of Zhao in China; a decisive Qin victory.
260 BC: Ashoka inscribes the Edicts of Ashoka.
258 BC: An Dương Vương overthrows the Hồng Bàng Dynasty in Viet Nam.
257 BC: Thục Dynasty takes over Viet Nam.
241 BC: First Punic War ends in Carthaginian defeat. Rome demands large reparations, and annexes Sicily and Corsica.
230 BC: The Chinese Qin State conquers Han.
230 BC: Simuka declares independence from Mauryan rule and establishes the Satavahana Empire.
227 BC: The attempted assassination of Ying Zheng (嬴政), king of Qin State, by Jing Ke (荊軻) from Yan failed.
225 BC: A large Gallic army is defeated by the Romans at the Battle of Telamon.
225 BC: The Chinese Qin State conquers Wei.
223 BC: The Chinese Qin State conquers Chu.
222 BC: The Chinese Qin State conquers Yan and Zhao.
221 BC: With the conquest of the State of Qi, Qin Shi Huang (秦始皇) unifies the whole of China into one empire that also included northern Vietnam, forming the Qin Dynasty.
218 BC: Second Punic War begins. Hannibal makes his famous Alpine crossing to invade Italy, the Roman heartland.
216 BC: Hannibal famously crushed the Roman legions at the Battle of Cannae.
214 BC: Qin Shi Huang (秦始皇) of the Chinese Qin Dynasty ordered construction of the Great Wall of China.
208 BC: Zhao Tuo (Triệu Đà) defeats the Vietnamese king An Dương Vương.
207 BC: Triệu Dynasty of Viet Nam is inaugurated.
206 BC – 202 BC: Civil war of the Chu-Han contention in China after the fall of the Qin Dynasty.
202 BC: Romans defeat Carthage, ending the Second Punic War. Carthage's territories are reduced to the city itself, and crippling reparations are demanded by Rome.
Indian traders regularly visited Arabia.
Scythians occupy Sogdiana, in modern-day Uzbekistan.
Han Dynasty of China was founded (202 BC–220 AD).
The Pharos of Alexandria is built.
Appearance of the Hopewell culture in Ohio, United States.
Teotihuacán, Mexico begun.
Appius Claudius Caecus, Roman statesman
Aratus of Sicyon, Greek statesman
Arsinoe II, co-ruler of Egypt
Ashoka, Mauryan ruler of India
Bai Qi (白起), Chinese general
Bindusara, ruler of the Mauryan Empire
Diodotus I, first ruler of Greco-Bactrian Kingdom
Emperor Gaozu of Han (高皇帝), founder of the Han Dynasty in China
Gaius Lutatius Catulus, Roman general
Hamilcar Barca, Carthaginian general and politician
Han Xin, Chinese general
Hannibal Barca, Carthaginian general and politician
Hanno the Great, Carthaginian politician
Hasdrubal Barca, Carthaginian general
Ilamcetcenni, Cholas ruler of South India
King Zhaoxiang of Qin, Chinese king of the Qin state
Lian Po, Chinese general
Li Bing (李冰), Chinese administrator and engineer
Li Mu, Chinese general
Li Si (李斯), Chinese Chancellor of the Qin Dynasty
Lü Buwei, Chinese merchant and Chancellor of Qin
Lin Xiangru, Chinese politician
Mago Barca, Carthaginian general
Manius Curius Dentatus, Roman general
Marcus Atilius Regulus, Roman general
Marcus Claudius Marcellus, Roman general
Marcus Porcius Cato, Roman statesman and writer
Masinissa, king of Numidia
Meng Tian, Chinese general
Modu Chanyu, Xiongnu chieftain
Philip V of Macedon, King of Macedonia
Ptolemy I, pharaoh of Egypt
Ptolemy II, pharaoh of Egypt
Pyrrhus of Epirus, King of Epirus
Publius Cornelius Scipio Africanus, Roman general and politician
Qin Shi Huang (秦始皇), Chinese Emperor
Quintus Fabius Maximus Verrucosus, Roman general and politician
Xanthippus of Carthage, Greek general
Wang Jian, Chinese general
Xiang Yu (項羽), Chinese rebel general against the Qin Dynasty
Xiao He, Chinese statesman and Chancellor of the Han dynasty
Zhang Liang, Chinese strategist and statesman
Zhao Tuo, Chinese military commander who conquered the Vietnamese Kingdom of Au Lac
Apollonius of Rhodes, Greek poet
Aratus, Greek poet
Callimachus, Greek poet and scholar
Gnaeus Naevius, Roman poet
Menander, Greek playwright
Menippus, Greek satirist
Song Yu (宋玉), Chinese poet
Theocritus, Greek poet
Qu Yuan (屈原), Chinese poet and scholar
Apollonius of Perga, Greek mathematician
Arcesilaus, Greek philosopher
Archimedes, Greek mathematician, physicist, and engineer
Aristarchus of Samos, Greek astronomer and mathematician
Aristyllus, Greek astronomer
Berossus Hellenistic Babylonian historian and astronomer
Conon of Samos, Greek astronomer
Demetrius of Phalerum, Greek philosopher and orator
Dicaearchus, Greek philosopher and scientist
Epicurus, Greek philosopher
Eratosthenes, Greek mathematician, geographer and astronomer
Euclid, Greek geometer
Han Fei (韓非), Chinese philosopher
Manetho, Hellenistic Egyptian historian
Mencius, Chinese philosopher
Philo of Byzantium, Greek mechanic
Pyrrho, Greek philosopher
Theophrastus, Greek philosopher
Timon of Phlius, Greek philosopher
Xun Kuang (荀況, Xun Li), Chinese philosopher
Zeno of Citium, Greek philosopher
Zenodotus, Greek grammarian
Eratosthenes accurately calculates diameter of the Earth using Camels and Shadows.
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 BC.
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 Ctesibius, a Greek engineer working in Alexandria.
Emperor Gaozu of Han China discovers an elaborate mechanical puppet theater in the treasury of the previous ruler Qin Shihuang.
The enormous Du Jiang Yan Irrigation System of China is engineered and constructed by Li Bing (李冰) in 256 BC.
Burial chamber, Tomb of the Reliefs, Cerveteri, is made.
Great Stupa, Sanchi, Madhya Pradesh, India, Maurya period, is founded by King Chandragupta Maurya.
Silk is exported to Europe from China.
Armillary spheres, models of objects in the sky developed by the Greeks, are in use as teaching tools.
3rd century BC Wikipedia
See: List of sovereign states in the 3rd century BC.