LONDON.- The 1326 marriage contract between Edward III and Philippa of Hainault leads Bonhams Fine Books and Manuscripts Sale in London on Wednesday 27 March. It is estimated at £100,000-150,000.

The contract, written on one skin of vellum, was the decisive factor in a carefully laid plot to invade England, raise a rebellion and depose the reigning monarch, Edward II.

The prime mover of these events was Isabella, wife of Edward II who plotted to unseat her husband and replace him with their 13-year-old son, the future Edward III. Sent to France in 1325 to negotiate with her brother King Charles IV, Isabella – known as the She-Wolf of France – refused to return to London, established a court-in-exile and arranged for her son to join her in Paris. The marriage contract with Philippa – who was around 11 years old – had one purpose only: to raise the money and men with which to invade England and depose Edward.

Isabella was motivated partly by revenge – she resented the king’s fondness for the company of Piers Gaveston and other young men – and partly by political considerations. Edward II was a weak king, and his reign was studded with disaster – the heavy defeat against the Scots at Bannockburn in 1314, the civil war with his barons, and the virtual surrender of power to one of his favourites, Hugh Despenser and his father.

Isabella and her lover Roger Mortimer invaded England in September 1326 with the troops provided under the terms of the marriage contract, They met little resistance, and within a few days Edward’s reign was effectively over. By January the following year, Edward had formally renounced the throne in favour of his son, with Isabella and Mortimer appointed joint regents. Weeks later Edward II was murdered in Berkeley Castle in Gloucestershire on the orders of Mortimer. Over the following two years, Isabella and Mortimer systematically abused their position to acquire estates and wealth, until Edward III asserted his authority in 1330 and had Mortimer arrested for treason and executed.

The marriage of Edward III and Philippa was happy and successful, producing 13 children and ending only with the queen’s death in 1369. Philippa was a popular figure and won admiration for persuading the king to pardon the Burghers of Calais, six civic dignitaries who had volunteered to face death in order to spare the rest of the townsfolk. Queen’s College Oxford is named in her honour.

Historian Felix Pryor who catalogued the document for Bonhams said, “This deed is an extraordinary survival from the middle ages, and few more potent relics of English history have been offered for sale. Without it there would have been no Black Prince, nor any of his numerous siblings, the disputing claims of whose descendants were to give rise to the Wars of the Roses in the following century, curtain-raiser to the Tudors and the modern, post-feudal, age. It is also a physical embodiment of open rebellion and the invasion of England less than a month later.”