Set into the gate piers of a school near the centre of Johnstown Bridge village are two square stone plaques, each roughly half a metre across, bearing the heraldic arms of two of the most consequential figures in late medieval and Tudor Ireland. That such objects ended up flanking a school entrance, rather than in a museum or a ruin, gives them an oddly domestic quality, easy to pass without a second glance.

One plaque carries the coat-of-arms of Gerald FitzGerald, the eleventh Earl of Kildare, a magnate whose family dominated Irish politics through much of the fifteenth and early sixteenth centuries. The other bears the arms of Sir Henry Sidney, who served as Lord Deputy of Ireland, the Crown's chief governor, during the reign of Elizabeth I. Writing in the late 1890s, the antiquarian O'Leary traced both plaques to Clonagh Castle, which lies about two miles to the west of the village. Armorial plaques of this kind were typically fixed to the walls or gateways of a castle to signal ownership, allegiance, or the commemoration of a building campaign, so their presence at Clonagh suggests some formal connection between the site and these two figures, though the precise circumstances are not recorded. How and when they were moved from the castle to their current position at the school is not clear, but their relocation is a fairly common fate for decorative stonework once a building falls into disuse or ruin.