Tang dynasty

18 June 618, at Chang'an — not Luoyang

Li Yuan deposed the child emperor Yang You and ascended the throne as the first Tang emperor in 618, at Chang'an, the western capital.

He named the new dynasty Tang after his hereditary fief and proclaimed Wude — "Military Virtue" — as his reign era. A scholarly reconstruction identifies the accession as the jiazi day of the fifth lunar month, converted as 18 June, and places the ceremony in the Taiji Hall.

Two things he did not do

He did not capture Luoyang. The Sui general Wang Shichong soon enthroned another Sui prince, Yang Tong, there, and Tang forces did not take the city until Wang Shichong capitulated in 621.

He did not have Emperor Yang murdered either. Yuwen Huaji's coup had already killed him at Jiangdu — and that news is what removed the remaining rationale for Li Yuan's façade of governing as a loyal Sui regent.

A quarter of an empire

Calling the day the end of the Sui is a dynastic convention. Competing Sui courts and claimants survived outside Chang'an, and more than 200 rebel organizations were active around the transition, of which only about ten were serious contenders for an enduring regime.

The new court's northwestern territory contained less than a quarter of the former Sui population.

Li Yuan also did not proclaim himself "Emperor Gaozu" — that is the temple name by which he became known after his death.