An obelisk (from the Greek work for "needle") is a thin, tall, four-sided monument having a small pyramid at the top. In ancient times there were made of a monolith, or single piece of stone.
The ancient Egyptians built many obelisks as tribute to the sun god Ra. They believed that the god resided in the structure. The earliest surviving obelisk was build by Senwosri I. of the XIIth Dynasty at Heliopolis. It is 68 feet tall. There are 27 ancient Egyptian obelisks still in existence, and also an unfinished obelisk taken from a quarry at Aswan. In ancient Egypt the obelisk symbolized the sun god Ra and during the brief religious reformation of Akhenaten was said to be a petrified ray of the aten, the sundisk. It was also thought that the god existed within the structure.
Modern architecture continues to make use of the obelisk. The largest obelisk in existence is the Washington Monument in Washington, D.C.