Middlesex (/ˈmɪdəlsɛks/, abbreviation: Middx) was a county in southeast England that is now mostly part of Greater London, with small sections in neighbouring counties. It was established in the Anglo-Saxon system from the territory of the Middle Saxons. The historic county included land stretching north of the River Thames from 3 miles (5 km) east to 17 miles (27 km) west of the City of London with the rivers Colne and Lea and a ridge of hills as the other boundaries. The largely low-lying county, dominated by clay in its north and alluvium on gravel in its south, was the second smallest by area in 1831.