An obelisk (UK: , from obeliskos; diminutive of obelos, "spit, nail, pointed pillar") is a tall, four-sided, narrow tapering monument which ends in a pyramid-like shape or pyramidion at the top. These were originally called "tekhenu" by the builders, the Ancient Egyptians. The Greeks who saw them used the Greek 'obeliskos' to describe them, and this word passed into Latin and then English. Ancient obelisks were often monolithic (that is, built with a single stone), whereas most modern obelisks are made of several stones and can have interior spaces.