OBELISK

An obelisk is a tall, narrow, four-sided, tapering monument which ends in a pyramid-like shape at the top.Obelisks were prominent in the architecture of the ancient Egyptians.The obelisk symbolized the sun god Amon Re, 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.The pyramid and obelisk would have been inspired by previously overlooked astronomical phenomena connected with sunrise and sunset: the zodiacal light and sun pillars respectively.

The Ancient Romans were strongly influenced by the obelisk form.Rome is the obelisk capital of the world. The most prominent is the 25.5 m/83.6 ft high 331 ton obelisk at Saint Peter's Square in Rome.

the most famous obelisks in Egypt are:

Pharaoh Tuthmosis I, Karnak Temple, Luxor
Pharaoh Ramses II, Luxor Temple
Pharaoh Hatshepsut, Karnak Temple, Luxor
Pharaoh Senusret I, Al-Masalla area of Al-Matariyyah district in Heliopolis, Cairo
Pharaoh Ramses III, Luxor Museum
Pharaoh Ramses II, Gezira Island, Cairo, 20.4 m[14]
Pharaoh Ramses II, Cairo International Airport, 16.97 m
Pharaoh Seti II, Karnak Temple, Luxor, 7 m
Pharaoh Senusret I, Faiyum (ancient site of Crocodilopolis), 12.9 m

Also the most mysterious of oblesiks is the Washington Monument in Washington DC, USA, measuring 555 feet 5.5 inches (169.29 m) in height, is the world's tallest true obelisk; completed in 1884. 

it may feature in dan browns next novel the lost symbol

(visit all the links in the post,loads of info)