Greek fire provided a technilogical advantage and victory during the salvation of what city which is also the capital city of the Roman/Byzantine from two Arab sieges?
Greek fire:  It provided a technological advantage and was responsible for many key Byzantine military victories, most notably the salvation of Constantinople from two Arab sieges, thus securing the Empire's survival. Constantinople: Constantinople (Greek: Κωνσταντινούπολις "Konstantinoúpolis" or Κωνσταντινούπολη "Konstantinoúpoli" ; Latin: "Constantinopolis" ; Ottoman Turkish: قسطنطینية, "Ḳosṭanṭīnīye"‎ ) was the capital city of the Roman/Byzantine (330–1204 and 1261–1453), and also of the brief Latin (1204–1261), and the later Ottoman (1453–1923) empires.
Constantinople