20 May 1021

Russo-Ukrainian war: Russia claimed full control of Mariupol after a nearly three-month siege.

A tornado struck Moore, Oklahoma, United States, killing 24 people and causing an estimated $2 billion of damage.

The first of two major earthquakes struck Northern Italy, resulting in seven deaths.

A team of researchers led by French virologist Luc Montagnier published their discovery of HIV, but were not then certain that it caused AIDS.

While attempting to land at Cairo International Airport, Pakistan International Airlines Flight 705 crashed for unknown reasons, killing all but 6 of the 121 people on board.

The first session of the National Diet opened in Tokyo, Japan.

The Luttra Woman (skull pictured), a bog body from the Early Neolithic period, was discovered near Luttra, Sweden.

World War II: German paratroopers began the Battle of Heraklion on the island of Crete, capturing the airfield and port in Heraklion ten days later.

With the signing of the Treaty of Jeddah, the United Kingdom recognized the sovereignty of Ibn Saud over Hejaz and Nejd, which later merged to become Saudi Arabia.

Representatives from seventeen countries signed the Metre Convention, which set up an institute for the purpose of coordinating international metrology and for coordinating the development of the metric system.

J. S. Bach led the first performance of his Pentecost cantata Erschallet, ihr Lieder at the chapel of Schloss Weimar.

Thomas Thorpe published the first copies of Shakespeare's sonnets, possibly without William Shakespeare's consent.

Ulysses, who would be famously depicted in a posthumous woodcut, landed in Lisbon, becoming the first of his species to visit Europe in a thousand years.

First Barons' War: English forces under William Marshal defeated French troops at the Battle of Lincoln.

According to the Anglo-Saxon Chronicle, King Æthelberht II of East Anglia was beheaded on the orders of Offa of Mercia.

The Picts defeated the Northumbrians at the Battle of Dun Nechtain, severely weakening the latter's power in northern Great Britain.

The First Council of Nicaea, the first ecumenical council of the Christian Church, was formally opened by Constantine the Great.

Russo-Ukrainian war: Russia claims full control of the Ukrainian city of Mariupol after a nearly three-month siege.

The International System of Units (SI): The base units are redefined, making the international prototype of the kilogram obsolete.

The government of Singapore authorises the controversial execution of convicted murderer Kho Jabing for the murder of a Chinese construction worker despite international pleas for clemency, notably from Amnesty International and the United Nations.

At least 27 people are killed and 50 others injured when a 6.0-magnitude earthquake strikes northern Italy.

Mamata Banerjee is sworn in as the Chief Minister of West Bengal, the first woman to hold this post.

An Indonesian Air Force Lockheed L-100 Hercules crashes in Magetan Regency, killing 99.

The independence of East Timor is recognized by Portugal, formally ending 23 years of Indonesian rule and three years of provisional UN administration (Portugal itself is the former colonizer of East Timor until 1976).