Those cages, fitted with wire grilles and locked from outside, were where readers were once secured with rare or valuable volumes to prevent theft, a measure that speaks plainly to how seriously the library's founders took the protection of their collection. The room itself has changed remarkably little, its dark oak shelves still carrying the original books in something close to their original arrangement.

Marsh's Library was begun in 1702, making it the oldest public library in Ireland. It takes its name from Narcissus Marsh, the Church of Ireland Archbishop of Dublin, who established it to provide scholars in the city with access to books that had previously been difficult or impossible to obtain. The building was designed by Sir William Robinson, who also built the Royal Hospital at Kilmainham, and it was constructed in the grounds adjoining St Patrick's Cathedral. The collection Marsh assembled runs to tens of thousands of volumes covering theology, medicine, law, and classical literature, many of them predating the library itself by a century or more. Jonathan Swift, who served as Dean of St Patrick's, was among those who used the library, and his annotations are said to appear in some of the surviving volumes.

The library is open to the public on a limited schedule, so checking current opening hours before visiting is worthwhile. It sits on St Patrick's Close, a short walk from the cathedral's west front, and the entrance is easy to miss if you are not looking for it. Once inside, the atmosphere is quiet and particular, not performatively old but simply preserved, the kind of place where the smell of aged paper and the creak of wooden floors do the work without any encouragement. Visitors can walk through the reading rooms and see the wired alcoves intact, along with display cases containing some of the more unusual items from the collection.