May 27.
893. Simeon I is crowned Emperor of the First Bulgarian Empire. Under his reign, which will last for about 30 years, this empire will reach the height of its power. By 1018, however, the last of the Bulgarian mountain retreats will have surrendered to the Byzantine Empire, headed by Basil II, "BulgarSlayer", and the empire is abolished.
For those who are curious, the Second Bulgarian Empire arises starting in 1185 when certain nobles break away, and will last until approximately 1400 when it is subjugated by the Ottoman Turks and its burgeoning empire.
1703. Tsar Peter the Great founds the city of Saint Petersburg, a/k/a Petrograd, a/k/a Leningrad.
The Church of the Savior on Spilled Blood, St. Petersburg:
1933. The Securities Act is signed into law.
1940. British troops desperately trying to reach the Dunkirk defensive perimeter get bottled up at a bridge over the Yser canal in the town of Poperinge. The Luftwaffe strafes the columns for several hours putting 80% of the vehicles there out of action. General Brooke (not yet Lord Alanbrooke) orders counterattacks to disrupt German operations. The Le Paradis massacre occurs, when an SS division machine guns 97 British prisoners. Most British troops arrive within the Dunkirk defensive perimeter by nightfall. Heavy bombing and artillery shelling of Dunkirk continues. Evacuations begin.
1941. The German battleship Bismarck is sunk, with nearly 2,100 men killed.
1942. The quality of the human race is greatly improved when Reinhard Heydrich is assassinated near Prague, Czechoslovakia, though it will take nearly a week for him to die from his injuries.
1962. The Centralia, Pennsylvania mine fire starts. It still burns to this day, and will likely go on for decades more.