Question: 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?

Context articles: Greek fire
List of wars involving Greece
Ravenna
Siege of Tyana
Siege of Constantinople (717–718)
Callinicus of Heliopolis
Constantinople
Byzantine–Hungarian War (1127–29)
Siege of Nicaea (727)
Springald

Greek fire was an incendiary weapon used by the Eastern Roman (Byzantine) Empire that was first developed .
 The Byzantines typically used it in naval battles to great effect, as it could continue burning while floating on water.
 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.
This is a list of known wars, conflicts, battles/sieges, missions and operations involving ancient Greek city states and kingdoms, Magna Graecia, other Greek colonies (First Greek colonisation, Second Greek colonisation, Greeks in pre-Roman Crimea, Greeks in pre-Roman Gaul), Greek Kingdoms of Hellenistic period, Byzantine Empire/ Byzantine Greeks, Byzantine Greek successor states of the Byzantine Empire, Kingdom of Greece and Greece between 3000 BC and the present day.
Ravenna (] , also locally ] ; Romagnol: "Ravèna" ) is the capital city of the Province of Ravenna, in the Emilia-Romagna region of Northern Italy.
 It was the capital city of the Western Roman Empire from 402 until that empire collapsed in 476.
 It then served as the capital of the Ostrogothic Kingdom until it was re-conquered in 540 by the Eastern Roman (Byzantine) Empire.
 Afterwards, the city formed the centre of the Byzantine Exarchate of Ravenna until the invasion of the Lombards in 751, after which it became the seat of the Kingdom of the Lombards.
The Siege of Tyana was carried out by the Umayyad Caliphate in 707–708 or 708–709 in retaliation for a heavy defeat of an Umayyad army under Maimun the Mardaite by the Byzantine Empire in c. 706.
 The Arab army invaded Byzantine territory and laid siege to the city in summer 707 or 708.
 The date is uncertain, as virtually each of the extant Greek, Arabic and Syriac parallel sources has in this respect a different date.
 Tyana initially withstood the siege with success, and the Arab army faced great hardship during the ensuing winter and was on the point of abandoning the siege in spring, when a relief army sent by Emperor Justinian II arrived.
 Quarrels among the Byzantine generals, as well as the inexperience of a large part of their army, contributed to a crushing Umayyads victory.
 Thereupon the inhabitants of the city were forced to surrender.
 Despite the agreement of terms, the city was plundered and largely destroyed, and according to Byzantine sources its people were made captive and deported, leaving the city deserted.
The Second Arab siege of Constantinople in 717–718 was a combined land and sea offensive by the Muslim Arabs of the Umayyad Caliphate against the capital city of the Byzantine Empire, Constantinople.
 The campaign marked the culmination of twenty years of attacks and progressive Arab occupation of the Byzantine borderlands, while Byzantine strength was sapped by prolonged internal turmoil.
 In 716, after years of preparations, the Arabs, led by Maslama ibn Abd al-Malik, invaded Byzantine Asia Minor.
 The Arabs initially hoped to exploit Byzantine civil strife and made common cause with the general Leo III the Isaurian, who had risen up against Emperor Theodosius III.
 Leo, however, tricked them and secured the Byzantine throne for himself.
Kallinikos or Latinized Callinicus (Greek: Καλλίνικος ) was a Byzantine architect and chemist from Heliopolis of Syria.
 He is credited with the invention of the Greek fire.
 According to Constantine Porphyrogenitus, Callinicus was a Syrian refugee who arrived in Byzantium in the time of Constantine IV and shared his knowledge of liquid fire with the Byzantines.
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.
 It was reinaugurated in 324 AD from ancient Byzantium as the new capital of the Roman Empire by Emperor Constantine the Great, after whom it was named, and dedicated on 11 May 330 AD.
A Byzantine–Hungarian War was fought between Byzantine and Hungarian forces on the Danube between 1127 and 1129.
 According to the Byzantine chronicler Niketas Choniates, the citizens of the Byzantine town Braničevo "attacked and plundered the Hungarians who had come to" the Byzantine Empire "to trade, perpetrating the worst crimes against them."
 Stephen II of Hungary broke into the empire in the summer.
 His troops sacked Belgrade, Braničevo and Niš, and plundered the regions around Serdica (Sofia, Bulgaria) and Philippopolis (Plovdiv, Bulgaria), before returning to Hungary.
 In response, Emperor John II marched against Hungary in 1128, where he defeated the royal troops in a battle at Haram, and "captured Frangochorion, the richest land in Hungary" (now in Serbia).
 Following his victory over the Hungarians John II launched a punitive raid against the Serbs.
 Dangerously for the Byzantines the Serbs had aligned themselves with Hungary.
 Many Serbian prisoners were taken, and these were transported to Nicomedia in Asia Minor to serve as military colonists.
 This was done partly to cow the Serbs into submission (Serbia was, at least nominally, a Byzantine protectorate), and partly to strengthen the Byzantine frontier in the east against the Turks.
 The Serbs were forced to acknowledge Byzantine suzerainty once again.
 In Hungary, the defeat at Haram undermined Stephen II's authority and he faced a serious revolt when two counts, named 'Bors' (possibly Boris Kalamanos) and 'Ivan', were declared kings.
 Both were eventually defeated, Ivan being beheaded and Bors fleeing to Byzantium.
 Stephen was unable to participate in any of the fighting because he was sick, recuperating in his homeland, according to John Kinnamos.
 John Kinnamos wrote of a second campaign by Stephen against the Byzantine Empire, when the Hungarian troops, supported by Bohemian reinforcements under the command of Duke Václav of Olomouc, took Braničevo by storm and destroyed its fortress.
 The Hungarians had renewed hostilities, possibly in order that King Stephen could be seen to reassert his authority, by attacking the Byzantine frontier fortress of Braničevo, which was immediately rebuilt by John.
 Further Byzantine military successes – Choniates mentions several engagements – resulted in a restoration of peace.
 Cinnamus describes a Byzantine reverse occurring before peace was established, which suggests that the campaign was not entirely one-sided.
 Hungarian records, however, agree with Choniates in indicating that King Stephen was again defeated and was consequently forced to negotiate a peace on Byzantine terms.
 Historian Ferenc Makk thinks that Emperor John II Komnenos was forced to retreat and sue for peace and that the treaty was signed in October 1129.
 The Byzantines were confirmed in their control of Braničevo, Belgrade, and Zemun and they also recovered the region of Syrmia (called Frangochorion in Choniates), which had been in Hungarian hands since the 1060s.
 The Hungarian pretender Álmos died in 1129, removing the major source of friction.
The Siege of Nicaea of 727 was an unsuccessful attempt by the Umayyad Caliphate to capture the Byzantine city of Nicaea, the capital of the Opsician Theme.
 Ever since its failure to capture the Byzantine Empire's capital, Constantinople, in 717–718, the Caliphate had launched a series of raids into Byzantine Asia Minor.
 In 727, the Arab army, led by one of the Caliph's sons, penetrated deep into Asia Minor, sacked two Byzantine fortresses and in late July arrived before Nicaea.
 Despite constant attacks for 40 days, the city held firm and the Arabs withdrew and returned to the Caliphate.
 The successful repulsion of the attack was a major boost for Byzantine emperor Leo III the Isaurian's recently initiated campaign to abolish the veneration of icons in the Empire; Leo claimed it as evidence of divine favour for his policy.
 The siege of Nicaea marks also the high point of the Umayyad raids, as new threats and defeats on their far-flung frontiers diverted Umayyad strength elsewhere, while Byzantine power gradually recovered.
A Springald, or espringal, is mechanical artillery device for throwing large bolts and less commonly stones or Greek fire.
 It is depicted in diagram in an 11th-century Byzantine manuscript, but in Western Europe is more evident in the late 12th century and early 13th century.
 It was constructed on the same principles as a Greek or Roman ballista, but with inward swinging arms.
 It was also known as a 'skein-bow', and was a torsion device using twisted skeins of silk or sinew to power two bow-arms.