Spear Of Destiny
Years later Lara recovered it from the U-boat ruins, after infiltrating a Russian submarine, whose crew were also searching for the spear. The volatile power of the spear also caused an explosion on the Russian submarine which sank afterwards. Lara escaped but the spear sank with the submarine.
Powers
It supposedly made an army invincible when wielded. The power from the spear however was very volatile and uncontrollable. Hence the spear would cause explosions if its power was disturbed. Lara probably did not attempt to retrieve the spear from the Russian wreckage of the submarine after witnessing its tremendous ability to destroy. The spear by far is the most potent artefact in the Tomb Raider Series.
Background
The real spear of destiny - also known as the Spear of Longinus and the Holy Lance - is one of very few artefacts in the Tomb Raider Game series to be based on Christian beliefs - it is supposedly the spear taken from Jesus' side when he died on the cross. Whether it truly exists is unknown - although many people have 'discovered' it over the years, only to be disproved and have it dismissed as a hoax. After WW2, a popular rumor abounded that Adolf Hitler had instigated the conflict to acquire the spear, or that the successes of the German Military during the early years of the war could be attributed to his already owning the spear. It was later rumored to have entered into American or Russian hands after the war or that it was even buried by the Nazis in Antarctica. Tomb Raider Chronicles seems to explore this theory and base it's Russia levels on it.
