A city-state is an independent sovereign city which serves as the center of political, economic, and cultural life over its contiguous territory. They have existed in many parts of the world since the dawn of history, including ancient poleis such as Athens, Sparta, Carthage and Rome, and the Italian city-states during the Middle Ages and Renaissance, such as Florence, Venice, Genoa and Milan.
With the rise of nation states worldwide, there remains some disagreement on the number of modern city-states that still exist; Singapore, Monaco and Vatican City are the candidates most commonly discussed. Out of these, Singapore is the largest and most populous, and is generally considered to be the last real city-state left in the world, with full sovereignty, international borders, its own currency, a robust military, and substantial international influence in its own right. The Economist refers to the nation as the "world's only fully functioning city-state".
Several non-sovereign cities enjoy a high degree of autonomy and are often confused as city-states. Hong Kong, Macau, and members of the United Arab Emirates—most notably Dubai and Abu Dhabi—are often cited as such.
Historical city-states included Sumerian cities such as Uruk and Ur; Ancient Egyptian city-states, such as Thebes and Memphis; the Phoenician cities (such as Tyre and Sidon); the five Philistine city-states; the Berber city-states of the Garamantes; the city-states of ancient Greece (the poleis such as Athens, Sparta, Thebes, and Corinth); the Roman Republic (which grew from a city-state into a vast empire); the Italian city-states from the Middle Ages to the early modern period, such as Florence, Siena, Ferrara, Milan (which as they grew in power began to dominate neighboring cities) and Genoa and Venice, which became powerful thalassocracies; the Mayan and other cultures of pre-Columbian Mesoamerica (including cities such as Chichen Itza, Tikal, Copán and Monte Albán); the central Asian cities along the Silk Road; the city-states of the Swahili coast; Ragusa; states of the medieval Russian lands such as Novgorod and Pskov; and many others.