When does the era begin?

This lesson asks you to place key events and periods of classical history in a chronological framework, for example on parallel timelines of Greece and Rome. The museum offers one case: how a dating system named for Alexander was traced to its real start, among the parts of the Greek world after his death. The rest of the framework, and the Roman side, are for your class to add. ¹

Find out what the start of the count is, and who counted from it. Then ask why people might have named an era for one reign when it starts elsewhere, and what you would write on a timeline so that nobody is confused.

Follow a dating argument step by step. In the record of the era of Alexander, al-Biruni explains that Philip ruled Macedonia for twenty-seven years, that Alexander was born to him of Olympias in the eighth year of his reign, and that Alexander reigned after his father twelve years and seven months. ² When Alexander died at Babylon, his realm was divided in three. ² Seleucus shared rule with Antiochus until he ruled alone at the end of the twelfth year of the son of Lagus; from then the Greeks began to date, and the era became known by Alexander's name though it starts in the thirteenth year after his death. ²

The records preserve no statement by al-Biruni of why he treated this era. They hold two things. The editor cites the passage to show that al-Biruni did not list eras thoughtlessly but examined their origins and the reasons for the historians' disagreements. ² And the record of al-Qanun al-Mas'udi reports, from the editor's quotation of the preface, that al-Biruni did not follow earlier zij-makers, who confined themselves to tabular settings and concealed how they had founded their rules, but joined to every procedure its reasons, so that the reader could approve or correct rather than imitate. ^{3 4} That is a purpose for the whole book, not for this era alone.

The record sets two readings of the era's start against each other. Al-Biruni says, as the editor quotes, that most people suppose it counted from the beginning of Alexander's reign, like the era of Yazdgird from his first year, and that the authors of the reasons of the zijes said the first year of his reign began on a Monday. ⁴ Al-Biruni's own account puts the start in the thirteenth year after Alexander's death. ² The record also notes a puzzle for the first reading: those authors found Ptolemy dating some observations from Alexander's death, which fell earlier than what they took for his accession, and they were perplexed. ⁴ The record gives al-Biruni's argument and no reply from the holders of the first reading.

The finding reaches the museum through three hands: al-Biruni's text, the editor of the Beirut edition who quotes it, and the record. The record says "as the editor quotes", so it does not show al-Biruni's whole passage. The authors of the reasons of the zijes who held the other view are not named, and their words are not given. The record also says that Macedonia went to Philip Arrhidaeus, from whom Theon's canon dates. ² The record thus names a second dating anchor in the zij tradition, and it holds no second author confirming al-Biruni's account of the era's start.

Al-Biruni argues from the lengths of reigns and the division of Alexander's realm, and the record holds no second author to check it. How far would you trust his count, and which step of his argument would you check first, and why?

• The era of Alexander (Seleucid era): al-Biruni's reckoning of the start, the three-way division of the realm, and who dated by whom.
• Al-Biruni: his life and works as the Encyclopaedia of Islam article gives them.
• al-Qanun al-Mas'udi: the book in which the argument appears, and its author's stated method.

Read The era of Alexander (Seleucid era). On a strip of paper, mark the three parts of the realm and the point from which the era counts.