Around 15 people were killed and 400 to 700 others injured when cavalry charged into a crowd demanding the reform of parliamentary representation in Manchester, England.

Historically, cavalry are groups of soldiers or warriors who fight mounted on horseback. Until the 20th century, cavalry were the most mobile of the combat arms, operating as light cavalry in the roles of reconnaissance, screening, and skirmishing, or as heavy cavalry for decisive economy of force and shock attacks. An individual soldier in the cavalry is known by a number of designations depending on era and tactics, such as a cavalryman, horseman, trooper, cataphract, knight, drabant, hussar, uhlan, mamluk, cuirassier, lancer, dragoon, samurai or horse archer. The designation of cavalry was not usually given to any military forces that used other animals or platforms for mounts, such as chariots, camels or elephants. Infantry who moved on horseback, but dismounted to fight on foot, were known in the early 17th to the early 18th century as dragoons, a class of mounted infantry which in most armies later evolved into standard cavalry while retaining their historic designation.

The Peterloo Massacre took place at St Peter's Field, Manchester, Lancashire, England, on Monday 16 August 1819. Eighteen people died and 400–700 were injured when the cavalry of the Yeomen charged into a crowd of around 60,000 people who had gathered to demand the reform of parliamentary representation.

Manchester is a city and metropolitan borough in Greater Manchester, England. It had an estimated population of 568,996 in 2022. Greater Manchester is the third-most populous metropolitan area in the United Kingdom, with a population of 2.92 million, and the largest in Northern England. It borders the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of Salford to the west. The city borders the boroughs of Trafford, Stockport, Tameside, Oldham, Rochdale, Bury and Salford.