Chronology outline for the foundation of Constantinople:
Thus we may formulate the following chronology outline, which of course is not entirely certain, but it is very likely:
September 18, 324: Victory of Constantine over Licinius in Chryssoupolis.
November 324: Constantine accords his son Constantius the title of Caesar while formally decides the foundation of Constantinople in the city of Byzantium, which he refurbishes. On this day, the ceremony of limitatio (defining the limits of the city) or of limitatio-inauguratio (?) took place, defining the new perimeter of Byzantium-Constantinople. The Emperor appears for the first time with a pearl diadem.
In 325 the major building projects start.
November 26, 328: Constantine is present at the ceremony of inauguratio, which marks the beginning of construction of the land walls.
May 11, 330: Celebration of the city's consrcration and dedication (consecratio-dedicatio). This date is fixed throughout Byzantine history as the date of birth of Constantinople.
330-336: Construction works were of course not complete in 330. Julian says that "It took Constantine nearly ten years to build the city that bears his name." Constantinople was undoubtedly a city under construction until his tricennalia, which was celebrated first in Nicomedia in 335, and then with glory in Constantinople in July of 336, while the vicenalia had only been celebrated in Rome.
Very soon, tradition gathered in a single year all this ten-year period and summarized it in a single celebration, that of May 11, 330.
After Dagron, G., Naissance d'une capitale. Constantinople et ses institutions de 330 à 451 (Paris 21984), p. 33 (in French).