 They immediately drew their swords and galloped towards St Peter's Field.One trooper, in a frantic attempt to catch up, knocked down Ann Fildes in Cooper Street, causing the death of her son when he was thrown from her arms; two-year-old William Fildes was the first casualty of Peterloo.Sixty cavalrymen of the Manchester and Salford Yeomanry, led by Captain Hugh Hornby Birley, a local factory owner, arrived at the house from where the magistrates were watching; some reports allege that they were drunk.