Rise and Fall of Roman Tetrarchy (+ 11 more historical events on this day!)

A Daily Dose of History: Events on this Day in History · May 21, 2026 · 8m

A Daily Dose of History (21 May 2026)

Today's historical events:

Roman Emperors Diocletian and Maximian appoint Galerius as Caesar to Diocletian, beginning the period of four rulers known as the Tetrarchy.

Syracuse, Sicily, is captured by the Muslim Aghlabids after a nine-month siege.

Pope John VIII gives blessings to Branimir of Croatia and to the Croatian people, considered to be international recognition of the Croatian state.

Sixteen-year-old Otto III is crowned Holy Roman Emperor.

Dušan's Code, the constitution of the Serbian Empire, is enacted by Dušan the Mighty.

Henry III of Castile…