Besides legend, the historical notes to be found concerning the city are numerous, however not precise and sometimes contradictory. These references are reported by Greeks writing before the time of Christ: Heroditus (V cent. B.C.), Hellanicus (V cent. B.C.), Polybius (II cent. B.C.), Dionysius of Alicarnasso (I cent. B.C.), and those who wrote after the time of Christ: Ptolemy (II cent. A.D.), Stefano Bizantino ( VI cent A.D.), in which the city appears at times with the name of Croton others Creston or Curton and the Latin writers of the first century before Christ, Virgil and Titus Livy who respetive call the city Corito and Cortona.
Modern historiography today seems to admit that Cortona was in origin and Umbran city, then conquered and enlarged by the Etruscans to become one of the most powerful lucomonie among the Etruscan confederacy together with Perugia and Arezzo. Evidence of its strategic position would be the extensive perimeter of its walls, the tombs of its royalty, all the archaelogical relics of this period which point out a rich city flourishing in artistic and industrial activity, minting a coing which from what has remained must be considered among the more perfect of ancient Etrusca.
Around the year 310 B.C., the greater part of the Etruscan lucomonie ( or city-states) were conquered by Rome. Cortona makes an agreement with the powerful city and enters into its realm and will have to witness what is described by Polybius and Livy as one of the most disastrous ambushes endured by the Roman army. The ambush took place in Cortona's territory and was concluded along the banks of Lake Trasimene.

In the era of the social war it probably was submitted (as was Arezzo) to the repression of Silla which was yet another blow leading to the loss of its strategic importance and economy.brWritten accounts of the times tell us however that in the first and second century after Christ, Cortona, as one of the thirty-eight Municipalities of the VII Region of Italy, the Roman Etruria, the administrative reform of the operative Empire of Augustus, had a flourishing political and administrative life.
It is due to this fact that, when during the second half of the third century of the Christian era the Roman Municipalities of Tuscany started to install dioceses for Christian bishops that Cortona probably became a bishopric. Due to the almost absolute lack of documentation, one must be cautious in making this assertion, however a document from the first half of the fifth century informs us of a martyrical memorial celebration which took place in May in the mortuary chapel for the anniversary of the matyr of Bishop Vicenzo. If Vicenzo was a bishop and buried in Cortona, one would be led to believe thaat Vincenzo was the bishop of Cortona and therefore that Cortona was a bishopric.