As you can see in LegioXXXUlpiaVictrix's post, Rome only started being planned in the second half of its existence, and long after it had started building an empire. As far as I know it wasn't a particularly large, let alone impressive city before the advent of the Principate proper (Augustus and onwards), with large numbers of the citizens of the Roman state living either on the Latin countryside or in coloniae spread throughout Italy and the empire. IIRC its growth to a city of a million with great, monumental architecture only started during the Pax Romana.