Emery postulates that after Thomas Parker purchased the castle in 1716, the latter's renovations probably affected more than three-quarters of the building, with the result that what stands at Shirburn today is "essentially an eighteenth-century interpretation of the medieval castle, following its original plan", although he allows that survivals from the original fourteenth-century structure include a "reasonable amount of the west range" (which would include the bulk of the main gate tower), the lower stages of two corner towers, and "possibly some ground-level walling internally", although he was unable to inspect the latter in person.Emery, 2006, pp. 153-154. The Victoria County History also suggests that: "The present south range may represent the medieval south range, with new windows inserted and with another range of rooms added to the south, outside the original outer wall." In a 1981 paper discussing the architecture of the present castle, authors Timothy Mowl and Brian Earnshaw suggest that the eighteenth-century rebuild intentionally incorporated round-arched, or neo-Norman, expressions of medievalism, "probably to assert a link with a supposed Norman foundation."Mowl, T. & Earnshaw, B. (1981). The origins of 18th-century neo-medievalism in a Georgian Norman castle. Journal of the Society of Architectural Historians 40(4): 289-294. doi:10.2307/989646 The same authors also point to Vanbrugh Castle, a London house designed and built by John Vanbrugh in 1719 for his own family, as a similar expression of neo-medievalism of around the same date, again with rounded windows, in contrast to the more pointed windows associated with the mid-18th century "Gothick" style of a few decades later. The rounded window style appears to have been used consistently in the Parker-era rebuild or renovation, including in all of the surviving inward-facing walls surrounding the courtyard, although from 1830, the effect was masked by the incorporation of more "standard" segmental-headed sash windows in the new external additions along several frontages. Considering all of the accounts presently available, it would seem to be the case that, at a time when his contemporaries had most recently been constructing their new country houses in the English Baroque style (or even neo-medieval, in the case of Vanbrugh Castle), Parker decided to purchase an actual, habitable 14th-century castle and construct his new residence entirely within it, at the same time adding new windows to the surviving medieval walls and towers in the Georgian style.
