The Priory was the English headquarters of the Order of St John of Jerusalem which combined religion, crusading military might and the care of the sick. The members of the order were also known as the Knights Hospitaller or the Knights of Malta. In 1312 this order merged with / took over the Knights Templar. The Priory was broken up in the Dissolution of the Monasteries. In 1877 set up the St John Ambulance Association.
A London Inheritance have two excellent posts on St John's Gate and the Priory of which it was once part.