The pre-eminent military Saint is Saint George, Great Martyr, Brigade Commander, Kallinikos and Trophy Bearer.
According to Pseudo-Kodinos in [Byzantine] court etiquette an emblem depicting Saint George on horseback was carried in the procession separately from those of the four great military martyrs, Demetrius, Procopius and the two Theodores.
“Festugiere (French Byzantine scholar), rightly associates several of the Saint’s interventions to save people with his military position such as the well-known miracle of saving the princess from the dragon.
However, the rescue of the young man from Mytilini is equally well known. Saint George had rescued other captives such as a young Paphlagona and the son of a general, Leo, as well as captives held by the Saracens and Bulgarians. Festugiere adds to these miracles [of military interest] the intervention of St. George to save the life of a horse wounded in battle in answer to the prayers of the soldier before the image of the Saint in his sanctuary at Lyda, and the resurrection of a soldier whose killers had been motivated by a desire to rob the money the soldier was carrying. These incidents remind us that the soldiers had a certain preference for the Saint.”
“Although there is evidence of the depiction of the Saint as a warrior before the iconoclastic period, the number of depictions of him as a warrior increases significantly after the iconoclasm, mainly in Cappadocia where military Saints were especially venerated. He was depicted as both the protector of soldiers and the conqueror of evil par excellence. They were placed in prominent positions such as at the entrances of temples or in front of the sanctuary, even in the arch.”
“The changes in the iconography of the Saint [from a Byzantine official to a Byzantine warrior] coincide with the changes in the concept of the Emperor who during the height of the Byzantine Empire from the reign of Nikephoros Phokas (963-969), John Tzimiskis (969 -976) and Basil II (976-1025) acquired the new quality of military courage and which was glorified on the battlefield.”
“Undoubtedly, the development of the cult of the Saint owes a lot to his adoption as a patron by the Byzantine emperors. Although not an invariable practice, impressive grants were usually made either to induce Saint George to protect the men for whom he was responsible in battle or as a reward for having already done so. Such sentiments are expressed in the Canon compiled by George Skylitzis in which you ask the help of the Saint in order to help the imperial army win the victory against the Scythians, Persians and barbarians.
“The Praecepta Militaria [mid-Byzantine military manual], usually attributed to Nikephoros Phokas, prescribed prayers to be said by soldiers daily, morning and evening, with severe penalties for those who did not participate. It is interesting that this highly successful general took religious practices in the army so seriously, as he was responsible for the image of the noble knight entering Byzantine script.”
“The Dioscuri provide an ancient precedent for intervention in battle. They fought the Romans at the Battle of Lake Regillus and announced victory by quenching their thirst at the Fountain of Zeus in Rome. The Apostles John and Philip joined the battle on the side of Emperor Theodosius as riders on white horses. Saint Andreas also intervened for the benefit of the city of Patras, of which he was also the patron, as well as Saints Demetrius and Theodore. However, Saint George intervened more often, but not necessarily alone and not only in favor of the Byzantines. His intervention to save the life of [general] Domnitsiolus, nephew of the emperor Phokas (602-610), was mentioned above [the Byzantine army had fallen into an ambush by the Persians]. He had also intervened in favor of Nikephoros Phokas in 961, before he became emperor, at the siege of Khandaka, together with Saints Demetrius, the two Theodoros and the Archangel Michael. He intervened again in favor of Andronikos II to whom he had promised victory when the emperor was kneeling and praying in front of an image of the Saint on horseback outside the chapel of the Theotokos of Nicopoiou (.).”
“Saint George was adopted by the Crusaders and mainly by the English. Edward III proclaimed him national patron in place of the Apostles Peter and Paul. The English invoked them against the French in the Hundred Years’ War. The Saint helped Alexander Nevsky, Grand Duke of Novgorod, against the Swedes in 1240 and against the Teutonic Knights in 1242.”
“In the last years of the Byzantine Empire, Saint George was needed more as a protector against the conquerors than as an ally in a battle that might have ended in victory. This explains the huge number of protective representations in late Byzantine temples. These were numerous in Transylvania where the indigenous Orthodox Romanian population sought protection against the Catholic Andeans, as well as in Crete which was vassal to Venice from 1204 to 1669.”
“[After the Latin and Turkish conquest the Greeks] needed protection from the conquerors above all. The protective function of military saints became relevant again. They are presented in countless representations, mainly on the facades or entrances of temples. These images were simple portraits but a popular pictorial type was that of St. George slaying an enemy or an obnoxious monster. This served as a linguistic code: in place of the monster, the Turks were meant.”
(Quotations are from the book: Christopher Walter, The Warrior Saints in Byzantine Art and Tradition, Ashgate 2003, pp. 109, 115-120, 126, 131, 280-281)