The county was significantly affected by the expansion of the metropolitan area of London in both the 18th and 19th centuries; such that from 1855 the south east was administered as part of the metropolis. The name means territory of the middle Saxons and refers to the reputed ethnic origin of its inhabitants. Its first recorded use was in 704 as Middleseaxan. The county lay within the London Basin and the most significant feature was the River Thames, which formed the southern boundary. The River Lee and the River Colne formed natural boundaries to the east and west. In the south west of the county the Thames meandered enough to make "Middlesex bank" more descriptively accurate than "north bank"; a distinction used during the The Boat Race. In the north the boundary was mostly formed by a ridge of hills broken by Barnet valley and a long protrusion of Hertfordshire into the county. The county was thickly wooded, with much of it covered by the ancient Forest of Middlesex. The highest point was the High Road by Bushey Heath at 502 feet (153 m), which is now one of the highest points in London.