Aristotle's idea of equality would have applied to all citizens who participate in the political life of the city-state in which they live. By doing so, they would have acquired the human virtues and excellences, as well as achieve their natural telos as a "political animal" (Aristotle, p. 4). Only within a city-state, citizens are able to participate and enhance their political and practical reason, thus reach their human telos. As such, the city-state is "among the things that exist by nature" (Aristotle, p. 4), and living in one is the only possible natural outcome for humans. However, the term citizen in Aristotle's perspective would not have applied to everyone, but it would have been rather limited within the city-state.
The city-state had been formed as a household, a partnership between "persons who cannot exist without one another" (Aristotle, 1252a27) and had later developed into a community of households, villages, the telos of which results in a chain of villages, city-state. It had come into existence to sustain our basic needs and it had stayed in order to support a better way of life.