No blog of Manchester's history should go long without mention of Peterloo. For details on the campaign to have the massacre noted more appropriately than just the above plaque, see: http://www.peterloomassacre.org/index.html
Wikipedia sums up Peterloo accurately, thus:
The Peterloo Massacre (or the Battle of Peterloo) occurred at St Peter's Fields, Manchester, England, on 16 August 1819, when cavalry charged into a crowd of 60,000 gathered at a meeting to demand the reform of parliamentary representation.
The end of the Napoleonic Wars in 1815 had resulted in periods of famine and chronic unemployment, exacerbated by the introduction of the first of the Corn Laws. By the beginning of 1819 the pressure generated by poor economic conditions, coupled with the lack of suffrage in northern England, had enhanced the appeal of political radicalism.
In response, the Manchester Patriotic Union, a group agitating for parliamentary reform, organised a demonstration to be addressed by the well-known radical orator Henry Hunt.
Shortly after the meeting began, local magistrates called on the military authorities to arrest Hunt and several others on the hustings with him, and to disperse the crowd.
Cavalry charged into the crowd with sabres drawn, and in the ensuing confusion, 15 people were killed and over 600 were injured.
The massacre was given the name Peterloo in ironic comparison to the Battle of Waterloo, which had taken place four years earlier.
Historian Robert Poole has called the Peterloo Massacre one of the defining moments of its age. In its own time, the London and national papers shared the horror felt in the Manchester region, but Peterloo's immediate effect was to cause the government to crack down on reform, with the passing of what became known as the Six Acts. It also led directly to the foundation of The Manchester Guardian newspaper (now The Guardian), but had little other effect on the pace of reform.
In a survey conducted by The Guardian newspaper in 2006, Peterloo came second to the Putney Debates as the event from British history that most deserved a proper monument or a memorial.
Peterloo is commemorated by a red plaque [above] close to the site, a replacement for an earlier blue one that was inadequate as it did not reflect the scale of the massacre.