No trace of it survives above ground, its precise location is unknown, and it does not appear on any map after 1691. What we do know comes largely from a handful of siege plans and a brief, matter-of-fact passage in a Williamite chronicle, yet taken together these sources sketch a structure that was, by any measure, a serious military work.

The fort was erected in June 1651 by Lieutenant-General Henry Ireton, the Cromwellian commander directing the siege of Limerick, and it appears on William Webb's plan of that siege identified in the map index as 'Coll Sadlier Quarters', a reference to Colonel Thomas Sadler who commanded a regiment of foot there. Sadler was no minor figure; he had taken over command of Colonel Arthur Culm's regiment after Culm was killed at Clonmel in May 1650, and he went on to serve as governor of Wexford in 1652 and later Galway in 1655. Webb's plan shows the fort as a quadrilateral with four corner bastions, a form sometimes called a bastioned trace, in which angled projections at each corner eliminate blind spots and allow defenders to cover the walls between them. It was surrounded by an external fosse, a defensive ditch, giving the whole work a star-shaped outline when seen from above. Entry was via a drawbridge on the north side, with a sallyport, a small concealed gate used for sorties, through the rampart on the southern quarter. Forty years later, in September 1691, the same position mattered again. The Williamite general Ginkel crossed the Shannon at Corbally and moved on the city via Thomond Bridge. The chronicler George Story recorded that the bridge approach was covered by two forts, and the one he describes as lying to the right, above musket-shot from the bridge, is almost certainly the Farranshone fort. After fierce fighting the Jacobite defenders were forced back across the bridge, but the city gates were closed against them. Story estimated that some 750 men were trapped under the walls, killed by Williamite fire or drowned in the Shannon.

Because the fort's exact position is unconfirmed, any coordinates attached to it in the archaeological record are treated as approximate, drawn from the map evidence rather than from ground survey. It appears to have been levelled in the early eighteenth century; it is absent from William Eyre's map of 1752 and from all subsequent Ordnance Survey mapping. A visitor to Farranshone today will find no earthwork, no plaque, and no obvious marker. The interest lies entirely in the documentary record, and for anyone inclined to stand on the approximate ground and read Story's account alongside Webb's plan, the landscape around Thomond Bridge and the northern bank of the Shannon does at least allow the geography of those two sieges to come into focus.