Holy Trinity's association today with a group of neighbouring churches is a timely reminder that over the longue durée parish churches have never evolved in isolation from each other but always functioned as part of larger interconnected church communities.
Holy Trinity was founded before the Norman Conquest and is recorded by 1066 as a church dedicated to Christ Church supported by a community of secular priests or canons. In the Domesday Book it was listed as one of five great northern churches together with the Minsters of Beverley, Durham and Ripon as well as York Minster as exempt from the payment of customary dues to either the king or the earl. In c.1089 this church was re-founded by its new Norman lord as a Benedictine priory served by a community of monks. It may be at that date a double church was constructed, with one half (Holy Trinity) providing a place of worship for the monastic community and a second (dedicated to St Nicholas) providing religious services to the lay community of the parish. However, almost no evidence survives of the fabric of either the pre- or immediate post-conquest churches on the site.
The date of the original foundation of the collegiate Christ Church is not certain but its precinct occupies a large site at the highest and most central point of the walled enceinte on the west bank of the Ouse. This mirrors the similarly prominent position of York Minster on the east bank of the Ouse — and indeed these two communities were the only collegiate churches in the City before the Norman Conquest. Both occupy sites of great importance in the Roman town plan: the Minster at the centre of the former walled garrison and Christ Church at the centre of the prosperous civilian town, the colonia, which was the centre of administration for the Roman province of Britannia Inferior.
Topographical analysis also suggests that the precinct of the now independent parish church of St Mary Bishophill Junior was once part of a single larger ecclesiastical enclosure around Holy Trinity that extended to over eight acres and (like the close around York Minster) may have contained a cluster of chapels around an early church foundation. Indeed the original precinct of Christ Church may have been even larger, extending across the site of Micklegate (a new road inserted into the town plan in the ninth or tenth centuries) as far as the original Roman road some metres further to the north-west and approximately underlying Tanner Row.
Certainly two small churches located between the roman road and Micklegate, one in Micklegate dedicated to St Gregory (often a tenth century dedication) and the other in North Street dedicated to All Saints, may once have formed part of this much extended precinct of Christ Church since by the twelfth century both were within the patronage of Holy Trinity Priory. Alternatively they could have been new small private church foundations of the tenth to eleventh century and the result of the growing commercial prosperity of York. Nevertheless their association with the lordship of Holy Trinity suggests strong territorial connections.
The existence of such a large precinct in such a prominent, even dominant, position in the Roman city and the grouping of Christ Church with a cluster of at least four immediately adjacent smaller churches all indicate that Christ Church (or Holy Trinity) may have been founded at about the same time as York Minster in the first phase of the conversion of Northumbria to Roman Christianity in the seventh century and was a major Anglican Minster. Some have suggested that this was the site of Alma Sophia, a sister church to York Minster founded in 780, although this is far from certain.
Even more speculative is the suggestion that Holy Trinity might conceivably have been a site of continuous Christian worship since the 4th century, when a bishop named Eborius is sometimes cited as evidence for a bishopric based in the late Roman city of York (Eboracum). Only archaeological excavation can ever reveal the full antiquity and importance of church foundations on the site.
The significance of Christ Church (later Holy Trinity) as a pre-Conquest Minster church is reinforced by the large extent of the territorial area subject to it. This may have included the whole of the walled city of York on the west bank of the Ouse and also several neighbouring extramural rural villages within the wapentake of the Ainsty such as Middlethorpe, Dringhouses, the Poppletons, Acomb, Knapton and Bilbrough. This is indicated both by the area of the estates associated with Christ Church in the Domesday survey and their close association with the rural estates of York Minster and the Archbishops of York, Holy Trinity's patronage of neighbouring smaller city churches by the twelfth century, and the existence of extramural rural parishes associated with those same intramural churches in the western portion of the city. The association of intramural churches with extramural parishes is often indicative of ancient Minster foundations, which were profoundly reformed by the establishment of new diocesan and parochial administrative structures across the twelfth century.
The reformation and re-foundation of Christ Church as a Benedictine priory after the Norman Conquest probably contributed locally to this general reform of a new parochial system, which was complete in York by the 1230s. This resulted in the subdivision of this original single large intra- and extra-mural parochial area associated with Christ Church into many smaller parishes each associated with one parish church, in particular Holy Trinity's neighbouring York churches of St Mary Bishophill Senior and Junior, St Clement, St Martin, St Gregory and All Saints North Street, several of whose parishes included detached rural extra- as well as intra-mural areas.