The Hundred-Horse Chestnut is the largest and oldest known chestnut tree in the world. Located on Linguaglossa road in Sant'Alfio, on the eastern slope of Mount Etna in Sicily — only 8 km (5.0 mi) from the volcano's crater — it is generally believed to be 2,000 to 4,000 years old. It is a sweet chestnut. Guinness World Records has listed it for the record of "Greatest Tree Girth Ever", noting that it had a circumference of 57.9 m (190 ft) when it was measured in 1780. Above ground, the tree has since split into multiple large trunks, but below ground, these trunks still share the same roots. An early 1895 image with a man next to the tree for perspective, shows it was closer to 10 m in diameter at breast height, rather than the claimed 18.5 m in diameter at breast height.

The chestnuts are the deciduous trees and shrubs in the genus Castanea, in the beech family Fagaceae. The name also refers to the edible nuts they produce. They are native to temperate regions of the Northern Hemisphere.