Paris (France, not Texas) is 53,188 hab/sq mi (20,544 hab/sq km in 2021).
Imperial Rome was said to be 1385 ha for 300,000 to 1,000,000 inhabitants (depending on sources, Marc Bloch giving 255,000). That gives us 21,600 hab/sq km or 56,000 hab/sq mi (for 300,000 hab). This is equivalent to current Paris (that has lost 1,000,000 inhabitants in 1 century), and required a whole country and part of an empire to be fed.
Around 400BC, Athens was roughly 160,000 inhabitants (including slaves) for roughly 3.5 sq km for 45,700 hab/sq km or 118,350 hab/sq mi. This is more than twice as densely populated as current Paris, and required whole Attica to be fed.