Jamaras
Jamara (الجَمَرَة) means a heap of stones, and its plural is Jamarat (الجَمَرات). The three Jamaras are located in Mina, near Mecca. It is said that it was here that Adam (a) forced away Satan, who was chasing him by throwing pebbles. Following this tradition, the pilgrims throw stones at each Jamara on 10th and 12th days of Hajj rituals. (see: Ramy al-Jamarat)
Jamaras were three pillars but now they are lengthened so they appear as three walls (apparently the old jamaras are located in the middle of the new ones).
References
- Makkah and Madinah: The Cities of Bounties & Blessings, Hajj and Ziarah Research Center