Lying in a graveyard on a gentle east-facing slope in County Kildare, the ruined church at Tully carries a curious double identity. Its square tower was already being called a castle by local people when Ordnance Survey officers noted it down in 1837, and the confusion is fitting: this was never quite an ordinary parish church. It was a preceptory of the Knights Hospitaller, one of the great military-religious orders of the medieval world, and its history involves nocturnal murders, a disputed right of sanctuary, and a sheela-na-gig carved onto a fragment of stone that still lies on the graveyard surface to the west of the ruins.

The Order of the Hospital of St John of Jerusalem, better known today as the Knights Hospitaller or the Knights of Malta, had its origins in a hospice founded in Jerusalem around 1070 to care for Christian pilgrims. The order established its Irish headquarters at Kilmainham in Dublin in 1174, from which it administered a network of subordinate houses called preceptories, essentially local estates that generated income and resources for the order's wider mission. The church at Tully was confirmed to the Hospitallers by Pope Innocent III in 1212, though it may have been founded at any point between 1174 and that date, and was probably built on or near the site of Tulach-Fobhair, an earlier ecclesiastical settlement connected to the monastery at Fore. A carved sandstone fragment with twelfth-century roll moulding hints that a Romanesque church may have preceded the Hospitaller foundation here, or else marks the order's own early construction on the site. By 1297, a Brother Robert was serving as prior of Tully, overseeing the church and an associated grange whose exact location has never been established. The medieval court rolls that survive from his tenure make for lively reading: a violent episode at the grange saw men dragged from their beds, killed, and buried without a coroner's view, their killers afterwards received at the preceptory house as if nothing had happened. A fugitive fled to the church for sanctuary; the seneschal Roger de Galweye hauled him out regardless, and gallows were subsequently erected on the road towards Offaly. Brother Robert, apparently trying to balance the church's legal right of sanctuary against the seneschal's authority, eventually sent the man back to the church, and then, as the record puts it with admirable brevity, "put himself on the country." The preceptory was dissolved in 1540 and its possessions catalogued in an inquisition held at Kildare that November, listing a castle or fortilage, arable land, a watermill, tenants' customary labour obligations including ploughdays and cartdays, and a cottage renting for two shillings. The last preceptor, John Walyngton, received a pension of £16 13s. 4d. from Henry VIII the following year. The lands passed through several hands thereafter, to Sir William Sarsfield in 1569, then to Henry Harrington, and by 1615 to Philip Hore under a grant from James I.