The hall, described as "perhaps the noblest monument in the Cinquecento style in England" was built 1853-6, commemorating the success of the Manchester-based Anti-Corn Law League and the campaign for free trade of the 1830s & 1840s. It's now the five-star Radisson Edwardian Manchester Hotel.

The circular plaque on the Peter Street side of the building indicates its greatest significance to the reform movement: this was the location of the St. Peter's Fields massacre - 'Peterloo'.
A reform meeting on this site (then open ground) on 16 August, 1819 was attended by 50,000 protesting against the lack of any parliamentary representation for the 200,000 people of Manchester and its satellite towns. They weren't 'revolutionaries' but cotton workers in their Sunday best, with their wives and children.
The Manchester magistrates lost their nerve and ordered the arrest of the main speakers. The Manchester Yeomanry were the first to respond - not mounted police with batons and training in crowd control, a part-time cavalry militia, allegedly drunk, who freely used their sabres and trampled people. Though also ordered to disperse the crowd, the professional soldiers of the 15th Hussars are credited as having restrained the Yeomanry somewhat, so that 'only' eleven people died and 400 were wounded.
The national government commended the magistrates. The meeting organisers were gaoled, as were journalists later reporting the massacre. An enquiry, begun a full year later, exonerated the Yeomanry.

Something of equal significance to some is that this was the concert venue (the home of the Hallé Orchestra, at that time) where Bob Dylan was heckled as "Judas!" in 1966.