On September 18

Five letters containing anthrax spores were mailed to various media outlets in the United States.

While posing as an aristocrat, Belgian serial killer Nestor Pirotte murdered an antiques dealer in Brussels, for which crime he was sentenced to death.

The wedding of King Constantine II of Greece and Princess Anne-Marie of Denmark took place in Athens.

Aeroflot Flight 213 crashed into a mountain near Chersky Airport, killing 32 people.

An aircraft crashed near Ndola in Northern Rhodesia, resulting in the deaths of 16 people, including United Nations secretary-general Dag Hammarskjöld.

Korean War: The Korean People's Army retreated from the Battle of the Pusan Perimeter after six weeks of fighting, marking the farthest that the KPA would advance in the war.

The Australian cricket team's Invincibles tour of England concluded; they had played 34 matches, including five Tests, without defeat.

World War I: The Central Powers' defeat at the Battle of Dobro Pole played a role in the Bulgarian withdrawal from the war and led to the subsequent liberation of Vardar Macedonia.

Five Chinese people were lynched outside of Pierce City in the Idaho Territory.

The Blackpool Illuminations (example pictured) in the English seaside town of Blackpool were switched on for the first time.

The Indianola hurricane dissipated over Mississippi after killing around eight hundred people in Texas.

Panic of 1873: The American bank Jay Cooke & Company declared bankruptcy, setting off a chain reaction of bank failures.

Nathaniel P. Langford of the Washburn–Langford–Doane Expedition first observed a geyser in the Wyoming Territory erupting at regular intervals, naming it Old Faithful (video featured).

The New York Times, the largest metropolitan newspaper in the United States, was founded.

The United States Congress passed the Fugitive Slave Act, decreeing that all escaped slaves be brought back to their masters.

Byzantine–Seljuk wars: Byzantine forces defeated their Seljuk opponents in the flanks of the nocturnal Battle of Kapetron, but learned of their Georgian allies' defeat in the centre the next morning.

Constantine the Great decisively defeated Licinius in the Battle of Chrysopolis, establishing Constantine's sole control over the Roman Empire and ending the Tetrarchy.

Nerva, the first of the "Five Good Emperors" of ancient Rome, came to power following the assassination of his predecessor Domitian.