Babel was built to stop the monsters within the dungeon from escaping. It was originally the same size as the buildings but was intentionally destroyed when the first Gods came down to earth. Those Gods later rebuilt it as it currently stands.
Babel is owned by the Guild to watch and take care of the dungeon. The first twenty floors are filled with Familia business, facilities, and money exchanges. The Hephaestus Familia has shops in floors 4-8. Above that are living areas of the most prominent Gods in Orario, known as the Private Rooms. Freya lives on the top floor of Babel.