Obelisks are a type of monument or monolith that have been used since ancient times. They are tall, four-sided, tapering structures that usually have a pyramidal top. Obelisks were originally used as religious symbols and were often placed in front of temples or other important buildings. They were also used to mark boundaries or to commemorate important events. Today, obelisks are still used as monuments, but they are also found in gardens and parks as decorative pieces.