The letter shown here is a reproduction of a poster seen in London in 1819, advertising a mass meeting in Finsbury Square in support of parliamentary reform. While such meetings were relatively commonplace in the mid-1810s this meeting was the cause of much government alarm. The meeting was convened just weeks after a similar event in Manchester had resulted in blood-shed and chaos: the so-called ‘Peterloo Massacre’ when yeomanry cavalry officers had attempted to break up the crowd by force, killing several people and injuring hundreds more in the process.
The advertised meeting moreover was called by Arthur Thistlewood, a chief agitator of the Spencean sect of radicals who advocated more violent forms of protest. Thistlewood had been previously arrested for inciting a riot at an earlier London meeting (although later acquitted), and was considered a dangerous and unpredictable individual by the government. Thistlewood was later executed for organising the Cato Street Conspiracy, a daring and audacious plot orchestrated in 1820 to murder the prime minister and his cabinet while they dined in London’s Mayfair.