The Holy Trinity Priory, also known as Christchurch Aldgate, was a priory of Austin canons (Black Canons) founded around 1108 by Queen Matilda of England.
The queen received advice and help in the foundation from Anselm of Canterbury, the Archbishop of Canterbury. The house was founded with clergy from St Botolph’s Priory in Colchester, and the first prior was Norman, who was the queen’s confessor.
By 1115 the entire soke, or liberty of East Smithfield (including the ward of Portsoken) was given by the Knighten Guilde to the church of Holy Trinity within Aldgate. The prior of the abbey was then to sit as an ex officio Alderman of London.
Matilda of Boulogne continued the close relationship between queenship and the priory. Two of her children were buried here and she took the prior as her confessor. In the 12th century the priory had a reputation as a centre of learning under Prior Peter of Cornwall.
The priory was dissolved in February 1532 when it was given back to King Henry VIII of England. The buildings and land associated with the priory were given, or sold, to prominent courtiers and City merchants. None of the buildings survive today except for some pointed arches within the office building on the corner of Aldgate and Mitre Street. Mitre Street itself follows roughly the line of the nave of the priory church, while Mitre Square corresponds roughly to the former cloister.