Sir Robert Dormer purchased the manor of Rousham in the mid 1630s and began at once to construct a house in the Jacobean style, using Oxfordshire stone.
The hall forms the heart of Rousham and has survived the alterations to the house in the 18th and 19th centuries.
The Civil War halted any further building work. Sir Robert was a Royalist and the lead-lined holes in the great oak door, through which muskets were aimed at Cromwell's troops, can still be seen.
Young Robert Dormer inherited Rousham in 1649. He did not make any alterations to the house apart from replacing the lead that the Parliamentary troops had stripped from the roof.
He married two heiresses and his second wife was a daughter of Sir Charles Cottrell, Master of Ceremonies at court.
In 1719 Colonel Robert Dormer inherited the estate from his father.
A few years later he began to transform the garden. His younger brother, General James Dormer, spent much time with him and was consulted at all stages.
The Colonel engaged the royal gardener, Charles Bridgeman, to design the garden and the work was almost complete when the Colonel died in 1737. General Dormer was the sixth son his parents and succeeded to Rousham when he was nearly sixty years old. The General moved in literary circles and was a great book collector. He amassed a considerable library at Rousham including works of English, French, Italian and Spanish literature.
In 1738 William Kent was called in by the General to continue the work on the garden.
Kent left Bridgeman's work intact but amplified it. In the four years that the General owned Rousham Park Kent created a garden of immense beauty for him.
Kent blended the garden visually with the landscape and transformed the river in the picturesque style.
He incorporated the medieval bridge and built a sham ruin, the 'Eyecatcher' on the sky-line. In the woodland garden he constructed a series of classical scenes with cascades, statuary, buildings and seats. These were designed to be viewed in sequence from a winding path.
Rousham has one of the earliest landscaped gardens in England and the only one of its time to survive unaltered.
Kent also remodelled the house. The roof was castellated and two shallow wings were added which provided the General with a library and the painted parlour. The latter room remains intact and contains some of Kent's furniture, his painted ceiling, wall brackets he designed to hold the General's collection of Italian bronzes and pictures Kent chose for the walls.
The General was the last of the Rousham Dormers. When he died in 1741 the estate was inherited by his first cousin Sir Clement Cottrell who assumed the additional name of Dormer. He was Master of Ceremonies at court and, although he loved Rousham Park, his court duties kept him in London most of the year.
Rousham soon became a popular tourist attraction and Kent had designed a gateway which allowed the public to enter the park from the road without going near the house. The visitors were supervised by the gardeners.
The estate was made over to Sir Clement's son Charles in the 1750s. Sir Charles was a noted agriculturist and made many improvements to the estate. However, his wife Jane decided to transform the library into a drawing room to make it suitable for entertaining.
General Dormer's huge collection of books were auctioned off in 1764 in a series of sales which continued over twenty successive evenings.
In the 1870s Clement Upton-Cottrell-Dormer, who had a eight sons and six daughters, employed the architect J.P. St Aubyn to double the central part of Rousham to make more room for his great family.
The garden, however, was left untouched and has been carefully tended by the succeeding generation of the family.