The spear appears in only one of the four Gospels. The Gospel of John, written in Greek toward the end of the 1st century CE, records that the soldiers who came to break the legs of the crucified men found Jesus already dead and did not break his bones, fulfilling the prophecy that not one bone of the righteous would be broken. Instead, one of the soldiers pierced his side with a spear, and at once blood and water came out. The Gospel gives no name to this soldier, no rank, and no aftermath. He is simply one of the executioners, and the spear is simply one of the weapons of the Roman army, a lonche, the Greek word for a thrusting spear or lance. But the blood and water that flowed from the wound became one of the most debated passages in Christian theology, interpreted as a sign of the sacraments of baptism and the Eucharist, and the wound itself became one of the Five Holy Wounds of Christ, the injuries that the resurrected Jesus showed to the doubting Thomas when he invited the disciple to place his hand in his side.

The soldier acquired his name centuries later. The apocryphal Gospel of Nicodemus, appended to late manuscripts of the 4th-century Acts of Pilate, calls him Longinus, a name probably derived from the Greek word for lance itself. In this tradition, Longinus was a centurion, a Roman officer in command of a hundred men, and he suffered from an eye ailment that was miraculously healed when the blood and water from Christ's side fell upon his face. The earliest visual record of the name appears in the Rabula Gospels of the late 6th century, where the inscription LOGINOS appears above the head of the soldier thrusting his spear into Christ's side. From that moment, Longinus became a saint in the Eastern and Western churches, and his spear became one of the most venerated relics in Christendom.

The history of the spear as a physical object is a history of empire. The earliest record of the lance as a relic comes from the late 6th century, when the pilgrim Antoninus of Piacenza wrote that it was displayed in the Basilica of Mount Zion in Jerusalem. The Jerusalem lance was taken by the Persians when they conquered the city around 615 CE, recaptured by the Byzantines, and eventually transferred to Constantinople, the new Christian capital built by Constantine the Great on the shores of the Bosphorus. At some point the point of the lance was broken off, and in the 13th century this fragment was given by the Byzantine ruler Baldwin II to King Louis IX of France, who kept it among the treasures of the French monarchy until it was lost during the French Revolution. The remaining portion of the lance fell to the Ottoman Turks when they conquered Constantinople in 1453, and in 1492 the Ottoman Sultan Bayezid II presented it to Pope Innocent VIII in exchange for the Pope's holding the Sultan's brother Djem as a political prisoner. That lance remains in St Peter's Basilica in Rome to this day, though the Catholic Church has never claimed that any of the several lances in its possession is definitively authentic.

The most famous of the rival claimants is the Vienna Lance, also called the Lance of Saint Maurice, kept in the Imperial Treasury at the Hofburg Palace. This lance became the coronation weapon of the Holy Roman Emperors, the rulers who claimed to be the successors of Charlemagne and the heirs of the Roman Empire. According to tradition, the lance passed from Longinus to Saint Maurice, the Theban legionary who was martyred with six thousand six hundred of his men in 287 CE for refusing to persecute Christians, and from Maurice to Constantine the Great, the first Roman emperor to embrace Christianity, who carried it into battle and used it to mark the boundaries of his new capital. Three centuries later, Pope Leo III gave the lance to Charlemagne, King of the Franks and founder of the Holy Roman Empire, on Christmas Day 800 CE, and Charlemagne was said to have carried it through forty-seven battles and to have died when he accidentally dropped it. Whether any of this is historically true, the lance became the physical symbol of imperial legitimacy, the weapon that proved heaven's favour rested upon the emperor who bore it. A metallurgical study in 2003 indicated that the body of the Vienna Lance dates from the 7th century CE, suggesting that it may have been part of the regalia of the Lombard kings of southern Italy before Charlemagne captured it in his conquest of the Lombard kingdom in the late 8th century, and that a Roman nail from the Crucifixion was later inserted into it to Christianise an already sacred weapon.

The most dramatic chapter in the lance's earthly history came during the First Crusade. In June 1098, the Crusader army was besieged inside the city of Antioch by a vastly superior Muslim force led by Kerbogha, the atabeg of Mosul. The Crusaders were starving, diseased, and outnumbered, and many were preparing to abandon the holy war. A peasant named Peter Bartholomew, serving in the army of Raymond of Toulouse, began to have visions of St Andrew the Apostle, who revealed to him that the Holy Lance was buried beneath the floor of the Church of St Peter in Antioch. Peter led a group of diggers to the spot, and they unearthed a rusty iron spearhead. The discovery electrified the army. The Crusaders believed that the lance that had pierced Christ would guarantee them victory, and the next morning they sallied out from the city and routed Kerbogha's army in one of the most improbable victories of the Middle Ages. Doubts about the relic's authenticity soon surfaced, and Peter Bartholomew was forced to undergo an ordeal by fire to prove his visions true. He walked through the flames and emerged apparently unharmed, but died twelve days later of his burns, and the lance he had found was gradually discredited. Yet the power of the belief had already changed history, and the Lance of Antioch remains one of the most vivid examples of how a relic could turn despair into triumph.

The Spear of Longinus crossed from Christian relic tradition into Arthurian mythology through the Grail romances of the 12th and 13th centuries. In the unfinished Perceval, the Story of the Grail by Chretien de Troyes, written around 1180, the hero witnesses a mysterious procession in the castle of the Fisher King, the wounded lord who cannot rise from his bed and whose lands have become a wasteland. In that procession, a squire carries a lance from whose tip a single drop of blood falls, running down the shaft to the hand of the bearer. Chretien does not identify this lance with the spear of Longinus, and the blood he describes has supernaturally destructive powers that do not match any Christian tradition. But the continuators of Chretien's poem, writing in the decades after his death, made the connection explicit: the bleeding lance was the Lance of Longinus, and its blood was the blood of Christ. In Wolfram von Eschenbach's German epic Parzival, composed in the early 13th century, the lance that appears in the Grail procession is described as streaming blood, and the wounded king Anfortas has been struck in the testicles by a poisoned weapon in a combat fought for the love of a woman not destined for him by the Grail. Only the lance that caused the wound can heal it, an echo of the Greek myth of Telephus, the king wounded by Achilles' spear and cured by the rust scraped from its blade. Wagner, in his 1882 opera Parsifal, fused these traditions into a single image: the same spear that pierced Christ on the cross is the weapon that wounded the Fisher King, and only the pure fool who understands through compassion can touch the spear and heal the wound it made.