Lisbon is a capital state.
Lisbon ( [ ˈlɪzbən ] Lisboa , [ liʒˈβoɐ ] ) is the capital and the largest city of Portugal , with a population of 552,700 within its administrative limits in an area of 100.05 km ² . Unlike most capital cities , Lisbon 's status as the capital of Portugal has never been granted or confirmed officially -- by statute or in written form . Its position as the capital has formed through constitutional convention , making its position as de facto capital a part of the Constitution of Portugal .