The oldest part of Parliament House is Parliament Hall, which the Town Council of Edinburgh, at its expense, had built as a permanent home for the Parliament of Scotland, and as such is the oldest extant purpose-built parliamentary building in the British Isles. It was completed in 1641 to the design of James Murray. The main interior feature is the elaborate oak trussed flat roof supported on carved stone corbels. Often described as a hammerbeam roof, it is a false hammerbeam, necessitated by the flat roof design. The internal ornamentation is provided by downward thrusting radial struts. The roof of the former Tron Kirk further down the High Street is similar in style but, because of the pitch of the roof, is a true hammerbeam. After the Act of Union 1707, the Parliament of Scotland was adjourned, and the building ceased to be used for its original function. The Hall was used for the sitting of courts, but in recent times has been subject to restoration work and now remains open as a meeting place for lawyers. Beneath Parliament Hall lies the Laigh Hall, of similar plan form but considerably less height.
Even while the old Parliament was still in existence, parts of the buildings were used for legal cases, and afterwards this became the main function of the building. The building is now used to house the College of Justice and other connected functions. In modern times, the building is chiefly used by the Court of Session, which hears civil cases, whilst most of the work of the High Court of Justiciary, which hears criminal cases, takes place in a dedicated building on the other side of the Royal Mile which formerly housed Edinburgh's Sheriff Court.
Libraries
The Advocates' Library was founded in 1682, and is currently located in a William Henry Playfair-designed building to the west of the south end of Parliament Hall. It remains a heavily used legal resource. As well as collecting legal works, it was also a deposit library, and in 1925 the non-legal books in their collection were given to the new National Library of Scotland, which is located next to the library, on George IV Bridge. To the west of the north end of Parliament Hall is The Signet Library. It is a private library, funded by members of The Society of Writers to Her Majesty's Signet, who are generally practising solicitors. Construction began in 1810 to a design by Robert Reid, and it presents a classical front to Parliament Square. This façade wraps around Parliament House as well, and replaced the existing Scottish baronial façade.