 Work to the designs of William Kent on the park commenced in 1729 , several years before the house was constructed . This event was commemorated by the construction in 1730 of the obelisk , 80 feet ( 24 m ) in height , standing on the highest point in the park . It is located over half a mile to the south and on axis with the centre of the house . An avenue of trees stretches over a mile south of the obelisk . Thousands of trees were planted on what had been windswept land ; by 1770 the park covered 1 @,@ 500 acres ( 6 @.@ 1 km2 ) . Other garden buildings designed by Kent are , near the far end of the avenue the Triumphal Arch , designed in 1739 but only completed in 1752 and the domed doric temple ( 1730 – 35 ) in the woods near the obelisk . Above the main entrance to the house within the Marble Hall is this inscription : 
