- 305 – Diocletian and Maximian retire from the office of Roman Emperor.
- 880 – The Nea Ekklesia is inaugurated in Constantinople, setting the model for all later cross-in-square Orthodox churches.
- 1328 – Wars of Scottish Independence end: Treaty of Edinburgh-Northampton – the Kingdom of England recognises the Kingdom of Scotland as an independent state.
- 1576 – Stefan Batory, the reigning Prince of Transylvania, marries Anna Jagiellon and they become the co-rulers of the Polish-Lithuanian Commonwealth.
- 1707 – The Act of Union joins the Kingdom of England and Kingdom of Scotland to form the Kingdom of Great Britain.
- 1751 – The first cricket match is played in America.
- 1753 – Publication of Species Plantarum by Linnaeus, and the formal start date of plant taxonomy adopted by the International Code of Botanical Nomenclature.
- 1776 – Establishment of the Illuminati in Ingolstadt (Upper Bavaria), by Jesuit-taught Adam Weishaupt.
- 1778 – American Revolution: The Battle of Crooked Billet begins in Hatboro, Pennsylvania.
- 1785 – Kamehameha, the king of Hawaiʻi defeats Kalanikupule and establishes the Kingdom of Hawaiʻi.
- 1786 – Opening night of the opera The Marriage of Figaro by Wolfgang Amadeus Mozart in Vienna, Austria.
- 1834 – The British colonies abolish slavery.
- 1840 – The Penny Black, the first official adhesive postage stamp, is issued in the United Kingdom.
- 1846 – The few remaining Mormons left in Nauvoo, Illinois, formally dedicated the Nauvoo Temple.
- 1848 – The Fraternity of Phi Gamma Delta is founded at Jefferson College in Canonsburg, Pennsylvania.
- 1851 – The Great Exhibition opens in London by Queen Victoria.
- 1852 – The Philippine peso is introduced into circulation.
- 1863 – American Civil War: The Battle of Chancellorsville begins.
- 1869 – The Folies Bergère opens in Paris.
- 1875 – Alexandra Palace reopens after the 1873 fire burnt it down.
- 1884 – Proclamation of the demand for eight-hour workday in the United States.
- 1886 – The Haymarket riots in Haymarket Square in Chicago, Illinois are the start of the general strike which eventually wins the eight-hour workday in the United States. These events are today commemorated as May Day or Labour Day in most industrialized countries.
- 1893 – The World's Columbian Exposition opens in Chicago.
- 1894 – Coxey's Army, the first significant American protest march, arrives in Washington, D.C.
- 1898 – Spanish-American War: The Battle of Manila Bay – the United States Navy destroys the Spanish Pacific fleet in the first battle of the war.
- 1900 – The Scofield mine disaster kills 200 in Scofield, Utah in what is to date the fifth-worst mining accident in United States history.
- 1901 – The Pan-American Exposition opens in Buffalo, New York.
- 1915 – The RMS Lusitania departs from New York City on her two hundred and second and final crossing of the North Atlantic. Six days later, the ship is torpedoed off the coast of Ireland with the loss of 1,198 lives, including 128 Americans, rousing American sentiment against Germany.
- 1925 – The All-China Federation of Trade Unions is officially founded. Today it is the largest trade union in the world, with 134 million members.
- 1927 – The first cooked meals on a scheduled flight are introduced on an Imperial Airways flight from London to Paris.
- 1927 – The Union Labor Life Insurance Company is founded by the American Federation of Labor.
- 1930 – The dwarf planet Pluto is officially named.
- 1931 – The Empire State Building is dedicated in New York City.
- 1940 – The 1940 Summer Olympics are cancelled due to war.
- 1941 – World War II: German forces launch Operation Mercury the largest airborne invasion to date in their bid to capture Crete.
- 1941 – World War II: German forces launch a major attack on Tobruk.
- 1945 – World War II: A German newsreader officially announces that Adolf Hitler has "fallen at his command post in the Reich Chancellery fighting to the last breath against Bolshevism and for Germany".
- 1946 – Start of 3 year Pilbara strike of Indigenous Australians.
- 1946 – The Paris Peace Conference concludes that the islands of the Dodecanese should be returned to Greece by Italy.
- 1948 – The Democratic People's Republic of Korea (North Korea) is established, with Kim Il-sung as president.
- 1950 – Guam is organized as a United States commonwealth.
- 1956 – The polio vaccine developed by Jonas Salk is made available to the public.
- 1956 – A doctor in Japan reports an "epidemic of an unknown disease of the central nervous system", marking the official discovery of Minamata disease.
- 1960 – Formation of the western Indian states of Gujarat and Maharashtra.
- 1960 – Cold War: U-2 incident – Francis Gary Powers, in a Lockheed U-2 spyplane, is shot down over the Soviet Union, sparking a diplomatic crisis.
- 1961 – The Prime Minister of Cuba, Fidel Castro, proclaims Cuba a socialist nation and abolishes elections.
- 1965 – Battle of Dong-Yin, a naval conflict between ROC and PRC, takes place.
- 1970 – Protests erupt in Seattle, Washington, following the announcement by U.S. President Richard Nixon that U.S. Forces in Vietnam would pursue enemy troops into Cambodia, a neutral country.
- 1971 – Amtrak (the National Railroad Passenger Corporation) is formed to take over U.S. passenger rail service.
- 1977 – 36 people are killed in Taksim Square, Istanbul, during the Labour Day celebrations.
- 1978 – Japan's Naomi Uemura, travelling by dog sled, becomes the first person to reach the North Pole alone.
- 1982 – The 1982 World's Fair opens in Knoxville, Tennessee.
- 1982 – Operation Black Buck begins. The RAF attack on the Argentine Air Force during Falklands War.
- 1983 – Greek composer Mikis Theodorakis is awarded the Lenin Peace Prize.
- 1987 – Pope John Paul II beatifies Edith Stein, a Jewish-born Carmelite nun who was gassed in the Nazi concentration camp at Auschwitz.
- 1989 – Disney-MGM Studios opens at Walt Disney World near Orlando, Florida, United States.
- 1991 – Rickey Henderson of the Oakland Athletics steals his 939th base, making him the all-time leader in this category. However, his accomplishment is overshadowed later that evening by Nolan Ryan of the Texas Rangers, when he pitches his seventh career no-hitter (breaking his own record).
- 1992 – On the third day of the 1992 Los Angeles riots, African-American activist, criminal, and victim of police beating Rodney King appears in public before television news cameras to appeal for calm and plead for peace, asking, "People, I just want to say, you know, can we all get along?".
- 1995 – Croatian forces launch Operation Flash during the Croatian War of Independence.
- 1997 – Tasmania becomes the last state in Australia to decriminalize homosexuality.
- 2000 – Philippine President Gloria Macapagal-Arroyo declares the existence of "a state of rebellion", hours after thousands of supporters of her arrested predecessor, Joseph Estrada, storm towards the presidential palace at the height of the EDSA III rebellion.
- 2003 – 2003 invasion of Iraq: In what becomes known as the "Mission Accomplished" speech, U.S. President George W. Bush declares that "major combat operations in Iraq have ended" on board the USS Abraham Lincoln off the coast of California.
- 2004 – Cyprus, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, and Slovenia join the European Union, celebrated at the residence of the Irish President in Dublin.
- 2006 – The Puerto Rican government closes the Department of Education and 42 other government agencies due to significant shortages in cash flow.
- 2007 – The Los Angeles May Day mêlée occurs, in which the Los Angeles Police Department's response to a May Day pro-immigration rally become a matter of controversy.
- 2008 – The London Agreement on translation of European patents, concluded in 2000, enters into force in 14 of the 34 Contracting States to the European Patent Convention.
Holidays and observances
- May Day, Labour Day, International Workers' Day, Day of the International Solidarity of Workers.
- Czech Republic – "National Love Day" – couples tend to flock to the memorial of the poet Karel Hynek Mácha in Prague and kiss.
- Lei Day – Hawaiian holiday for the Lei.
- Beltane, Lá Bealtaine, the first day of Summer in modern Ireland was celebrated by the Celts, and is now also celebrated by Neopagans and Wiccans.
- Kazakhstan - Unity Day.
- Maharashtra Day (Maharashtra Divas) – Maharastra, India.
- Marshall Islands - Constitution Day.
- Northern Europe – Walpurgis Night.
- Roman Empire – all-female festival in honour of Bona Dea.
- Roman Empire – fourth and last day of the Floralia in honour of Flora.
- United States – Law Day, U.S.A., Loyalty Day.
- Feast of Saint Joseph the Worker
- Saint James the Less.
- Saint Philip the Apostle.
- Saint Andeol.
- Saint Asaph
- Saint Brieuc.
- Saint Sigismund of Burgundy.
- Saint Theodulf.
- Saint Augustin Schoeffer
Traditional May Day celebrations
May Day is a cross-quarter day, associated with the Celtic festival of Beltane and the Germanic festival of Walpurgis Night. May Day falls exactly half of a year from November 1, another cross-quarter day which is also associated with various northern European pagan and neopagan festivals such as Samhain. May Day marks the end of the uncomfortable winter half of the year in the Northern hemisphere, and it has traditionally been an occasion for popular and often raucous celebrations, regardless of the locally prevalent political or religious establishment.
As Europe became Christianized the pagan holidays lost their religious character and either changed into popular secular celebrations, as with May Day, or were replaced by new Christian holidays as with Christmas, Easter, and All Saint's Day. In the twentieth century, many neopagans began reconstructing the old traditions and celebrating May Day as a pagan religious festival again.
The earliest May Day celebrations appeared in pre-Christian Europe, with the festival of Flora the Roman Goddess of flowers, the Walpurgis Night celebrations of the Germanic countries. It is also associated with the Gaelic Beltane. Many pagan celebrations were abandoned or Christianized during the process of conversion in Europe. A more secular version of May Day continues to be observed in Europe and America. In this form, May Day may be best known for its tradition of dancing the Maypole and crowning of the Queen of the May. Various Neopagan groups celebrate reconstructed (to varying degrees) versions of these customs on 1 May.
The day was a traditional summer holiday in many pre-Christian European pagan cultures. While February 1 was the first day of Spring, May 1 was the first day of summer; hence, the summer solstice on June 25 (now June 21) was Midsummer. In the Roman Catholic tradition, May is observed as Mary's month, and in these circles May Day is usually a celebration of the Blessed Virgin Mary. In this connection, in works of art, school skits, and so forth, Mary's head will often be adorned with flowers. Fading in popularity since the late 20th century is the giving of "May baskets," small baskets of sweets and/or flowers, usually left anonymously on neighbours' doorsteps.
May Day has been celebrated in Ireland since pagan times as the feast of Beltane and in latter times as Mary's day, bonfires are lit to mark the coming of summer and to banish the long nights of winter.
 United Kingdom
Traditional English May Day rites and celebrations include Morris dancing, crowning a May Queen and celebrations involving a Maypole. Much of this tradition derive from the pagan Anglo-Saxon customs held during "Þrimilci-mōnaþ" (the Old English name for the month of May meaning Month of Three Milkings).
May Day has been a traditional day of festivities throughout the centuries. With Christianity came agricultural feasts such as Plough Sunday (the first Sunday in January), Rogationtide, Harvest Festival and May Day. It is most associated with towns and villages celebrating springtime fertility and revelry with village fetes and community gatherings. Since May 1st is the Feast of St Philip & St James, they became the patron saints of workers. Seeding has been completed by this date and it was convenient to give farm labourers a day off. Perhaps the most significant of the traditions is the Maypole, around which traditional dancers circle with ribbons.
The May Day Bank Holiday was traditionally the only one to affect the state school calendar, although new arrangements in some areas to even out the length of school terms mean that the Good Friday and Easter Monday Bank Holidays, which vary from year to year, may also fall during term time.
In Oxford, it is traditional for revellers to gather below Magdalen College tower to listen to the college's choir for what is called May Morning. It is then thought to be traditional for some Oxford University students to jump off Magdalen Bridge into the River Cherwell. However this has actually only been fashionable since the 1970s. In recent years the bridge has been closed on 1 May to prevent people from jumping, as the water under the bridge is only 2 feet (61 cm) deep and jumping from the bridge has resulted in serious injury in the past yet there are still Oxford Univeristy students who insist on climbing the barriers and leaping into the water, causing injury. 
In Durham, students of the University of Durham gather on Prebend's Bridge at 5am to see the sunrise and enjoy pagan festivities, including folk music, dancing and a BBQ. This is emerging as a Durham tradition.
A good example of more traditional May Day festivities is still witnessed in Whitstable, Kent where the Jack in the Green festival was revived in 1976 and continues to lead an annual procession of morris dancers through the town on the May Bank Holiday. A separate revival occurred in Hastings in 1983 and has become a major event in the town calendar. Padstow also holds its annual 'Obby 'Oss festival. A traditional Sweeps Festival is performed over the May bank holiday in Rochester, Kent where the Jack In the Green is woken at dawn on the 1st of May by Morris dancers.
The Maydayrun involves thousands of motorbikes taking a 55-mile (89 km) trip from London (Locksbottom) to the Hastings seafront, East Sussex. The event has been taking place for almost 30 years now and has grown in interest from around the country, both commercially and publicly. The event is not officially organised; the police only manage the traffic, while volunteers manage the parking.
 Cornwall - South West England
Padstow in Cornwall holds its annual 'Obby-Oss' day of festivities. This is believed to be one of the oldest fertility rites in the UK; revellers dance with the Oss through the streets of the town and even through the private gardens of the citizens, accompanied by accordion players and followers dressed in white with red or blue sashes who sing the traditional 'May Day' song. The whole town is decorated with springtime greenery, and every year thousands of onlookers attend. Prior to the 19th century distinctive May day celebrations were widespread throughout West Cornwall and have recently been revived in St. Ives and in 2008 will be revived in Penzance.
Kingsand, Cawsand and Millbrook in Cornwall celebrate Flower Boat Ritual on the May Day bank holiday. A model of the ship The Black Prince is covered in flowers and is taken in procession from the Quay at Millbrook to the beach at Cawsand where it is cast adrift. The houses in the villages are decorated with flowers and people traditionally wear red and white clothes. There are further celebrations in Cawsand Square with Morris dancing and May pole dancing.
In St Andrews, some of the students gather on the beach late on April 30 and run into the North Sea at sunrise on May Day, occasionally naked. This is accompanied by torchlit processions and much elated celebration.
Both Edinburgh and Glasgow organize Mayday festivals and rallies. In Edinburgh, the Beltane Fire Festival is held on the evening of May eve and into the early hours of May Day on the city's Calton Hill.
 Mainland Europe
On May 1st, 1561, King Charles IX of France received a lily of the valley as a lucky charm. He decided to offer a lily of the valley each year to the ladies of the court. At the beginning of the 20th century, it became custom on the 1st of May, to give a sprig of lily of the valley, a symbol of springtime. The government permits individuals and workers' organisations to sell them free of taxation. It is also traditional for the lady receiving the spray of lily of valley to give a kiss in return. Now, people may present loved ones with bunches of lily of the valley or dog rose flowers 
In rural regions of Germany, especially the Harz Mountains, Walpurgisnacht celebrations of Pagan origin are traditionally held on the night before May Day, including bonfires and the wrapping of maypoles, and young people use this opportunity to party, while the day itself is used by many families to get some fresh air. Motto: "Tanz in den Mai!" ("Dance into May!"). In the Rhineland, a region in the western part of Germany, May 1 is also celebrated by the delivery of a tree covered in streamers to the house of a girl the night before. The tree is typically from a love interest, though a tree wrapped only in white streamers is a sign of dislike. On leap years, it is the responsibility of the females to place the maypole, though the males are still allowed and encouraged to do so.
In Hawaii, May Day is also known as Lei Day, and is normally set aside as a day to celebrate island culture in general and native Hawaiian culture in particular. While it was invented by a poet and a local newspaper columnist in the 1920s, it has since been adopted by state and local government as well as by the residents, and has taken on a sense of general spring celebration there. The first Lei Day was proposed in 1927 in Honolulu. Leonard "Red" and Ruth Hawk composed "May Day is Lei Day in Hawai'i," the traditional holiday song. Originally it was a contemporary fox trot, later rearranged as the Hawaiian hula song performed today.
May Day was also celebrated by some early European settlers of the American continent. In some parts of the United States, May Baskets are made. These baskets are small and usually filled with flowers or treats and left at someone's doorstep. The basket giver would ring the bell and run away. The person receiving the basket would try to catch the fleeing giver. If they caught the person, a kiss was to be exchanged.
Modern May Day ceremonies in the U.S. vary greatly from region to region and many unite both the holiday's "Green Root" (pagan) and "Red Root" (labor) traditions. Among the largest is the May Day Parade and Pageant created by In the Heart of the Beast Puppet and Mask Theatre, an event that has happened every year since 1975 in Minneapolis and now attracts some 35,000 people.
May 1 also is recognized in the U.S. as Law Day.
 International Workers' Day
May Day can refer to various labour celebrations conducted on May 1 that commemorate the fight for the eight hour day. May Day in this regard is called International Workers' Day, or Labour Day. The idea for a "workers holiday" began in Australia in 1856. With the idea having spread around the world, the choice of May 1st became a commemoration by the Second International for the people involved in the 1886 Haymarket affair.
The Haymarket affair occurred during the course of a three-day general strike in Chicago, Illinois that involved common laborers, artisans, merchants, and immigrants. Following an incident in which police opened fire and killed four strikers at the McCormick Harvesting Machine Co. plant, a rally was called for the following day at Haymarket Square. The event remained peaceful, yet towards the end of the rally, as police moved in to disperse the event, an unknown assailant threw a bomb into the crowd of police. The bomb and resulting police riot left at least a dozen people dead, including seven policemen. A sensational show trial ensued in which eight defendants were openly tried for their political beliefs, and not necessarily for any involvement in the bombing. The trial lead to the eventual public hanging of seven anarchists. The Haymarket incident was a source of outrage from people around the globe. In the following years, memory of the "Haymarket martyrs" was remembered with various May Day job actions and demonstrations.
As such, May Day has become an international celebration of the social and economic achievements of the labour movement. Although May Day received its inspiration from the United States, the U.S. Congress designated May 1 as Loyalty Day in 1958 due to the day's appropriation by the Soviet Union. Alternatively, Labor Day traditionally occurs on the first Monday in September in the United States. People often use May Day as a day for political protest, such as the million people who demonstrated against far-right candidate Jean-Marie Le Pen in France, or as a day for protest against government actions, such as pro-immigrant rallies across the United States.