Metropolis

A metropolis is a word that means a very big city, that usually has over 500,000 people living in it. A metropolis often has many smaller towns and cities inside its area. 
The word began in ancient Greece, originally meaning the city or state of origin of a colony. Later it came to mean the seat of a Bishop who also supervised the Church in other cities, or a city regarded as a center of some specified activity, or a large and important city. In India a "metropolis" is a city with more than a million people.
Old Uses
In the past many large cities were called metropolitan due to their size or importance; such as: Alexandria, Angkor, Antioch, Athens, Babylon, Baghdad, Beirut, Benares, Byblos, Carthage, Constantinople, Corinth, Damascus, Ephesus, Great Zimbabwe, Harappa, Jerusalem, Kangla, Nanjing, Nineveh, Macchu Picchu, Mohenjo-Daro, Rome, Sarai, Side, Syracuse, Tenochtitlan, Teotihuacan, Tikal, Tyre, Xian and Ur.
Modern Metropolises.
The modern metropolises are increasing day by day in this world since pre-21st century.