|Millennium:||1st millennium BC|
|100 BC by topic|
|Gregorian calendar||100 BC|
|Ab urbe condita||654|
|Ancient Egypt era||XXXIII dynasty, 224|
|- Pharaoh||Ptolemy X Alexander, 8|
|Ancient Greek era||170th Olympiad (victor)¹|
|Balinese saka calendar||N/A|
|Chinese calendar||庚辰年 (Metal Dragon)|
2597 or 2537
— to —
辛巳年 (Metal Snake)
2598 or 2538
|Coptic calendar||−383 – −382|
|Ethiopian calendar||−107 – −106|
|- Vikram Samvat||−43 – −42|
|- Shaka Samvat||N/A|
|- Kali Yuga||3001–3002|
|Iranian calendar||721 BP – 720 BP|
|Islamic calendar||743 BH – 742 BH|
|Minguo calendar||2011 before ROC|
|Seleucid era||212/213 AG|
|Thai solar calendar||443–444|
27 or −354 or −1126
— to —
28 or −353 or −1125
Year 100 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Marius and Flaccus (or, less frequently, year 654 Ab urbe condita). The denomination 100 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.
- Consuls: Lucius Valerius Flaccus, Gaius Marius (Marius's sixth consulship).
- Manius Aquillius celebrates an ovation for victories in the Second Servile War.
- Lucius Appuleius Saturninus, a tribune, passes a law to redistribute land to military veterans. The law requires that all senators swear to abide by it. Quintus Caecilus Metellus Numidicus refuses and is exiled. He goes to Rhodes to study philosophy.
- Late summer–autumn: Saturninus stands for tribune again for the following year, and is elected. His associate, the praetor Gaius Servilius Glaucia, attempts to stand for the consulship (illegally, as praetors cannot immediately become consul). A rival candidate, Gaius Memmius, is found murdered by agents of Saturninus and Glaucia, who are declared public enemies by the Senate. The Senate issues the senatus consultum ultimum, and Marius, as consul, defeats his former ally in battle in the Forum. Saturninus and his followers surrender on condition that their lives are spared, but they are stoned to death with roof tiles in the Curia Hostilia by renegade senators.
- The building of the Sanctuary of Fortuna Primigenia, Palestrina, Italy, is begun. The model of it is now kept at the Museo Archeologico Nazionale, Italy (approximate date).
- Tigranes II of Armenia is placed on Armenian throne by the Parthians in exchange for the cession of "seventy valleys". (approximate date)
- Peasants revolt under Emperor Wu of Han. The Great Wall is extended out into the Gobi Desert, and sections of the wall are detached with signalling towers.
- Gandhara and Punjab are ruled by the Indo-Greek king Demetrius III Aniketos.
- A History of China is written by Sima Qian (approximate date).
- Olmec III period ends in Southeastern Mexico.
- Joachim, father of Mary, the mother of Jesus
- Julius Caesar, Roman general and politician (d. 44 BC)
- Titus Labienus, Caesar's chief lieutenant in the conquest of Gaul (d. 45 BC)
- Cornelia Africana, mother of Tiberius Gracchus (b. c. 190 BC)
- Gaius Memmius (tribune), Roman politician
- Gaius Servilius Glaucia, Roman politician
- Lucius Appuleius Saturninus, Roman politician
- Theodosius of Bithynia, Greek astronomer and mathematician (b. c. 160 BC)
- Salvius Tryphon, Rebel slave
|Wikimedia Commons has media related to 100 BC.|
- There is some dispute over the year of Caesar's birth. Some scholars have made a case for 101 or 102 BC as the year of his birth, based on the dates that he held certain magistracies, but scholarly consensus favors 100 BC. Similarly, some scholars prefer 12 July for the day of his birth, but others give 13 July. Goldsworthy, p. 30, Ward, Heichelheim, & Yeo p. 194. For a source arguing for 12 July, see Badian in Griffin (ed.) p.16