During the 1916 Easter Rising, the City Hall was used as a garrison for the Irish Citizen Army. Sean Connolly seized the building using a key which he obtained as he worked in the motor department and had access to the building. There were 35 people based here, mostly women. It was in this area where the first casualty of the rising, a guard named James O’Brien, occurred at Dublin Castle and he was shot by Sean Connolly while on duty. In total, the entire siege lasted about 12 hours.