On May 20

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.

In deciding Romer v. Evans, the U.S. Supreme Court struck down a constitutional amendment in Colorado that prevented protected status under the law for homosexuals or bisexuals.

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, 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.

By the Treaty of Jeddah, the United Kingdom recognised the sovereignty of King Abdulaziz of Saudi Arabia (pictured) 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.

A British squadron under Charles Marsh Schomberg defeated a French force off Tamatave, Madagascar, that was attempting to reinforce the French garrison on Mauritius.

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.

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 (depicted), the first ecumenical council of the Christian Church, was formally opened by Constantine the Great.