11 (eleven) is the natural number following 10 and preceding 12. It is the first repdigit. In English, it is the smallest positive integer whose name has three syllables.
Copper engraving of a hendecagon, by Anton Ernst Burkhard von Birckenstein (1698)
12 (twelve) is the natural number following 11 and preceding 13. Twelve is a superior highly composite number, divisible by the numbers 2, 3, 4, and 6.
Ancient Hittite relief carving from Yazılıkaya, a sanctuary at Hattusa, depicting twelve gods of the underworld
Image of the globular cluster Messier 12 by Hubble Space Telescope