<P> The city maintained independence as a city - state until it was annexed by Darius I in 512 BC into the Persian Empire, who saw the site as the optimal location to construct a pontoon bridge crossing into Europe as Byzantium was situated at the narrowest point in the Bosphorus strait . Persian rule lasted until 478 BC when as part of the Greek counterattack to the Second Persian Invasion of Greece, a Greek army led by the Spartan general Pausanias captured the city which remained an independent, yet subordinate, city under the Athenians, and later to the Spartans after 411 BC . A farsighted treaty with the emergent power of Rome in c. 150 BC which stipulated tribute in exchange for independent status allowed it to enter Roman rule unscathed . This treaty would pay dividends retrospectively as Byzantium would maintain this independent status, and prosper under peace and stability in the Pax Romana, for nearly three centuries until the late 2nd century AD . </P> <P> Byzantium was never a major influential city - state like that of Athens, Corinth or Sparta, but the city enjoyed relative peace and steady growth as a prosperous trading city lent by its remarkable position . The site lay astride the land route from Europe to Asia and the seaway from the Black Sea to the Mediterranean, and had in the Golden Horn an excellent and spacious harbour . Already then, in Greek and early Roman times, Byzantium was famous for its strategic geographic position that made it difficult to besiege and capture, and its position at the crossroads of the Asiatic - European trade route over land and as the gateway between the Mediterranean and Black Seas made it too valuable a settlement to abandon, as Emperor Septimius Severus later realized when he razed the city to the ground for supporting Pescennius Niger's claimancy . It was a move greatly criticized by the contemporary consul and historian Cassius Dio who said that Severus had destroyed "a strong Roman outpost and a base of operations against the barbarians from Pontus and Asia". He would later rebuild Byzantium towards the end of his reign, in which it would be briefly renamed Augusta Antonina, fortifying it with a new city wall in his name, the Severan Wall . </P> <P> Constantine had altogether more colourful plans . Having restored the unity of the Empire, and, being in the course of major governmental reforms as well as of sponsoring the consolidation of the Christian church, he was well aware that Rome was an unsatisfactory capital . Rome was too far from the frontiers, and hence from the armies and the imperial courts, and it offered an undesirable playground for disaffected politicians . Yet it had been the capital of the state for over a thousand years, and it might have seemed unthinkable to suggest that the capital be moved to a different location . Nevertheless, Constantine identified the site of Byzantium as the right place: a place where an emperor could sit, readily defended, with easy access to the Danube or the Euphrates frontiers, his court supplied from the rich gardens and sophisticated workshops of Roman Asia, his treasuries filled by the wealthiest provinces of the Empire . </P> <P> Constantinople was built over six years, and consecrated on 11 May 330 . Constantine divided the expanded city, like Rome, into 14 regions, and ornamented it with public works worthy of an imperial metropolis . Yet, at first, Constantine's new Rome did not have all the dignities of old Rome . It possessed a proconsul, rather than an urban prefect . It had no praetors, tribunes, or quaestors . Although it did have senators, they held the title clarus, not clarissimus, like those of Rome . It also lacked the panoply of other administrative offices regulating the food supply, police, statues, temples, sewers, aqueducts, or other public works . The new programme of building was carried out in great haste: columns, marbles, doors, and tiles were taken wholesale from the temples of the empire and moved to the new city . In similar fashion, many of the greatest works of Greek and Roman art were soon to be seen in its squares and streets . The emperor stimulated private building by promising householders gifts of land from the imperial estates in Asiana and Pontica and on 18 May 332 he announced that, as in Rome, free distributions of food would be made to the citizens . At the time, the amount is said to have been 80,000 rations a day, doled out from 117 distribution points around the city . </P>

Why was the capital of the roman empire moved
find me the text answering this question