British Museum Plan

Foundation (1753)
On 7 June 1753, King George II gave his Royal Assent to the Act of Parliament which established the British Museum.^[b] The British Museum Act 1753 also added two other libraries to the Sloane collection, namely the Cottonian Library, assembled by Sir Robert Cotton, dating back to Elizabethan times, and the Harleian Library, the collection of the Earls of Oxford. They were joined in 1757 by the "Old Royal Library", now the Royal manuscripts, assembled by various British monarchs. Together these four "foundation collections" included many of the most treasured books now in the British Library including the Lindisfarne Gospels and the sole surviving manuscript of Beowulf.^[c]

Montagu House, c. 1715
The British Museum was the first of a new kind of museum – national, belonging to neither church nor king, freely open to the public and aiming to collect everything. Sloane's collection, while including a vast miscellany of objects, tended to reflect his scientific interests. The addition of the Cotton and Harley manuscripts introduced a literary and antiquarian element and meant that the British Museum now became both National Museum and library.
Cabinet of curiosities (1753–1778)

The Rosetta Stone on display in the British Museum in 1874
The body of trustees decided on a converted 17th-century mansion, Montagu House, as a location for the museum, which it bought from the Montagu family for £20,000. The trustees rejected Buckingham House, on the site now occupied by Buckingham Palace, on the grounds of cost and the unsuitability of its location.
With the acquisition of Montagu House, the first exhibition galleries and reading room for scholars opened on 15 January 1759. At this time, the largest parts of collection were the library, which took up the majority of the rooms on the ground floor of Montagu House and the natural history objects, which took up an entire wing on the second state storey of the building. In 1763, the trustees of the British Museum, under the influence of Peter Collinson and William Watson, employed the former student of Carl Linnaeus, Daniel Solander to reclassify the natural history collection according to the Linnaean system, thereby making the Museum a public centre of learning accessible to the full range of European natural historians. In 1823, King George IV gave the King's Library assembled by George III, and Parliament gave the right to a copy of every book published in the country, thereby ensuring that the museum's library would expand indefinitely. During the few years after its foundation the British Museum received several further gifts, including the Thomason Collection of Civil War Tracts and David Garrick's library of 1,000 printed plays. The predominance of natural history, books and manuscripts began to lessen when in 1772 the museum acquired for £8,410 its first significant antiquities in Sir William Hamilton's "first" collection of Greek vases.