A larger image of Longinus, in the Nea Moni Church, Chios, Greece, c.1049-55AD.
Longinus depicted in the Nea Moni Church, Chios, Greece. No name for the soldier who pierced Christ's side during the crucifixion is given in the Gospels; the name Longinus is found in the pseudepigraphal Gospel of Nicodemus that was appended to the apocryphal Acts of Pilate.
The Nea Mone (New Monastery) on Chios, founded before 1042, was richly endowed by Constantine IX Monomachos (r. 1042-55), and its church, with fine mosaics and colored marbles, seems to have been finished during his reign. 67
67. C. Bouras 1982; Mouriki 1985.
C. Bouras 1982 Charalambos Bouras. NeaMoni on Chios: History and Architecture. Athens, 1982.
Mouriki 1985 Doula Mouriki. The Mosaics of NeaMoni on Chios. Trans. Richard Burgi. 2 vols. Athens, 1985.
pp. 5-19 "Byzantine Society and Civilization" by Speros P. Vryonis, Jr. in Art and Culture of the Middle Byzantine Era A.D. 843-1261 Edited by Helen C. Evans and William D. Wixom, The Metropolitan Museum of Art, New York.
In Crucifixion iconography, originally only two figures flanked the dead Christ, that is, the Virgin Mary and St. John the Apostle. An extended version came in favour in the eleventh century. The added personages included the Roman centurion, Longinius, the first gentile to recognise Christ’s divinity.
The best known depiction is this beautiful mosaic in the monastery church of Nea Moni on the island of Chios, shown [above] .
The appearance of the major Biblical figures (saints, apostles etc.) is governed by strict rules in Byzantine iconography, and they are always dressed in Antique clothing, but the minor figures are usually dressed in the current style (an obvious example are Solomon and other rulers, who are clad in imperial vestments). This was presumably to make their identity ‘readable’ even by an illiterate viewer, by dressing them in clothing recognisably appropriate to ther status or profession.
Longinius is normally depicted richly dressed, in a style similar to the military saints - with a cape, usually a shield, and often a weapon and corslet, the model of a contemporary Byzantine army officer. Longinius usually lacks a halo. A consistent but puzzling feature, one yet to be satisfactorily explained, is his white hood or turban - similar ones are worn by Jewish elders in Byzantine religious art.
Several recent popular works  have declared that soldiers of the Varangian Guard were prototypes for the depiction of Longinius. There is not the slightest evidence for such a deduction.
Longinius was a Roman centurion, the Romaioi (Byzantines) were proud of their continuity with the Empire of Rome, so it would only make sense to dress Longinius as a native soldier, not a barbarian bodyguard .
 A. Grabar, ‘Byzantine Painting.’ Skira: New York 1953.
 For example, the Osprey militaria series. PB. [Byzantine Icon, 11th century, referenced on p26, MAA 89 Byzantine Armies 886-1118 by Ian Heath & Angus McBride, Osprey]
 My feeling is that it is most likely that he is given the uniform of a low-ranked Byzantine officer - possibly the leader of 100 men, an hekatontarch (a rank attested in 10th cent. military manuals). PB.
Source: Relics Of The Varangians by Peter Beatson
The Crucifixion and the Holy Women at the Sepulchre, folio 13r, The Rabbula Gospels Evangelia characteribus Syriacis exarata, Syria, 6th Century|
Crucifixion scene in the Chludov Psalter, Byzantine, Moscow, Historical Museum MS 129, 9th century
Crucifixion scene in the Psalter of Theodore of Caesarea, Byzantine, 11th century, British Library Add MS 19352
Crucifixion scene in the Hidden Church (Sakli Kilise), 11th century, Cappadocia, Turkey, showing Byzantine soldiers, by Steven Lowe
Centurion and soldiers deviding the cloths, Byzantine Icon, 11th century, held in Germany
Fresco of the Centurion at the Crucifixion, Katholikon at the monastery of Panagia Mavriotissa, Kastoria, Greece, c.1260AD
The Crucifixion, folio 124r of The T'oros Roslin Gospels of Armenia, 1262AD, Walters Ms. W.539
Byzantine Crucifixion scene in 14th century wall paintings, Church of Panagia Phorbiotissa, Asinou, Cyprus