The third foundation collection of The British Museum and The British Library is the Harleian Library. Robert Harley (1661-1724), 1st Earl of Oxford and Earl Mortimer, began this collection in October of 1704 when he acquired 600 manuscripts from the collection of the antiquary Sir Simonds d’Ewes (1602-1650), 1st Baronet.
Harley and his father had been active participants in the so-called Glorious Revolution. A M.P. for Radnor, Wales in the Parliament of England (1690-1707) and the Parliament of Great Britain (1707-1711) who served as Speaker of the House of Commons (1701-1705) and held multiple high positions under Queen Anne – Northern Secretary (1704-1708), Chancellor of the Exchequer (1710-1711), Lord High Treasurer (1711-1714) – he was effectively her premier. He helped bring about the unification of the Kingdom of Scotland with the Kingdom of England (and Principality of Wales) with the Act of Union (1707) and ended British involvement in the War of the Spanish Succession with the Treaty of Utrecht (1713).
In 1708, the scholar Humfrey Wanley (1672-1726) became librarian for the Harleys with the title keeper. Wanley was one of the original members of the Society of Antiquaries in 1707 (re-founded in 1717). The British Library states, “His diary (British Library Lansdowne MSS. 771-772) and letters are an important resource for describing the acquisition of individual manuscripts, and for understanding the growth of the collection as a whole.”
Robert Harley’s son, Edward Harley (1689-1741), Lord Harley took an active role in building the collection from 1711 onward. That decade saw the Harleys acquire several groups of English manuscripts. Starting around 1717, the Harleys began using agents in Continental Europe to make en bloc purchases of manuscripts from French, German, and Italian sources.
A consummate intriguer and astute manipulator of public opinion, Robert Harley managed to oust Sidney Godolphin (1645-1712), 1st Earl of Godolphin from power in 1710, two years after they had influenced Queen Anne to dismiss him. In 1711, she made him an earl and appointed him Lord High Treasurer.
Yet, in 1714, Henry St. John (1678-1751), 1st Viscount Bolingbroke, convinced Queen Anne to dismiss Harley while she was on her deathbed. Under King George I, Harley spent two years imprisoned in the Tower of London.
Edward Harley, 2nd Earl of Oxford and Earl Mortimer, is the eponym of London’s Harley Street and Oxford Street. Like his father (and grandfather) before him, Edward Harley represented Radnor in the House of Commons.
He did so from 1711 to 1714. Then he represented Cambridgeshire from 1722 until his father died in 1724, at which time he inherited his father’s titles and entered the House of Lords.
Lord Oxford was a bibliophile and patron of the arts who counted the writer Jonathan Swift (1667-1745) and poet Alexander Pope (1688-1744) amongst his friends. He was also a great landowner and real estate developer.
In terms of building the Harleian Library collection, the family benefited in the 1720s from auctions held in London of both British and foreign collections.
In 1713, he married Lady Henrietta Holles (1684-1755), daughter of John Holles (1662-1711), 1st Duke of Newscastle-upon-Tyne (second creation) and his wife, Margaret Cavendish (1668-1716), Duchess of Newscastle-upon-Tyne. Margaret’s parents were Henry Cavendish (1630-1691), 2nd Duke of Newcastle-upon-Tyne (first creation), and his wife, Frances Pierrepont (1630-1695), Duchess of Newcastle-upon-Tyne.
Lord and Lady Oxford had two children. Henry Cavendish Harley, Lord Harley, died in infancy. His sister, Margaret Cavendish Harley (1715-1785), Lady Margaret Harley, inherited much of her parents’ wealth, but her father’s titles passed to a cousin. In 1734, she married William Bentinck (1709-1762), 2nd Duke of Portland.
At that time, she became Margaret Cavendish Bentinck, Duchess of Portland. She possessed wealth that rivaled that of kings. With her husband, she had six children.
In 1753, Henrietta, Countess of Oxford and Countess Mortimer and her daughter Margaret Cavendish Bentinck, Duchess of Portland, sold the Harleian Library to the Crown for £10,000, a fortune in that era, but not the full monetary value of the collection and half as much as the Crown paid for the larger collections of Dr. Sloane. Today, The British Library’s Harleian Collection includes over 7,000 manuscript volumes, over 14,000 original legal documents, and 500 rolls.
The British Library states, “Although most are in European languages, including a sizeable number in Greek, the library also includes items in Hebrew and in various Oriental languages.”
Descriptions and digital images of more than 2000 manuscripts in the Harleian collection are being added progressively to the British Library’s online Catalogue of Illuminated Manuscripts, courtesy of a generous grant by the Getty Foundation.
When the British Museum formed in 1753, the trustees moved Sloane’s books from his Chelsea manor house to Montagu House (also spelled Montague House) on Great Russell Street in Bloomsbury, the first home of the British Museum, along with his other collections. The trustees acquired this chateau, the former London residence of the Dukes of Montagu, in 1759.
 King Charles I knighted Simonds d’Ewes in 1626 and made him a baronet in 1643. A Puritan, Sir Simonds d’Ewes, M.P., took the side of the Parliamentarians in the revolution called the English Civil War. He represented Sudbury in the Long Parliament from 1640 until Pride’s Purge in 1648, after which he retired from politics.
 On his death in 1862, their son William Henry Cavendish Cavendish-Bentinck (1738-1809), who had used her husband’s subsidiary title Marquess of Titchfield as a courtesy title, became the 3rd Duke of Portland and she became the Dowager Duchess of Portland. He would serve as Chancellor of the University of Oxford and as Prime Minister of the United Kingdom of Great Britain in 1783 and as Prime Minister of the United Kingdom of Great Britain and Ireland from 1807 to 1809.