One of my relatives, Dominick Fanning, was the Mayor of Limerick three times. He took part in the great Rebellion and was executed in 1651. He ended up with his head hanging above St. John’s gate for several years. How would I find out where this St. John’s gate was or is located? Was it in Limerick, London, or someplace else?
It was in Limerick. Specifically the Garryowen area, Garryowen being an anglicised version of Garraí Eoin which translates as Garden of John.
Not sure where exactly it was located as far as I know there is no trace left of it but there might be someone in /r/ireland, /r/irishhistory or /r/limerickcity who can give more info.
Incidentally the "great rebellion" is commonly know as the Irish Confederate Wars, an 11 year war comprising the Irish part of the war of the three kingdoms, it ended with the Cromwellian conquest, which is what the 1651 siege of Limerick was part of, although Cromwell himself had returned to England by then.