During the Crucifixion of Christ, a Roman Soldier was said to have stabbed him with a spear, a common practice to hasten death involving, I believe, opening up an artery in the leg.
|Longinus the Centurion. Russian icon by Fyodor Zubov, 1680.
The spear incident itself is referred to in the New Testament of John, later a man identified as Nicodemus gave this unknown soldier a name. Nicodemus work is called the "Apocryphal Gospel of Nicodemus" in 715 ce. and likely composed by several authors due to the changing styles in it's script.
Later illustrations in manuscripts and several locations claiming to house the spear all point to various sources in antiquity of acquiring it none of whom claim singular authenticity. Like most of this kind of thing it is highly doubtful any such genuine artifact exists.
The spear itself has been referred to as the "Spear of Destiny", the "Holy Lance" and the "Lance of Longinus".
Longinus subsequently has been promoted to a saint as Christianity's 1st convert, several traditions celebrate his feast day. These include the Roman Catholic, Eastern Orthodox, Coptic Orthodox and Armenian Apostolic churches.
After the 10th century the legend grew to include that Longinus was a blind Roman centurion who thrust the spear into Christ's side at the crucifixion. Some of Jesus's blood fell upon his eyes and he was healed thus affirming his faith in the savior's divinity.