Divine Source

The Divine Source is an ancient artifact of mysterious origins. It was discovered by Jacob during the era of the Byzantine Empire. After gazing upon it, he finds himself to be healed from grievous injuries and to live without aging. This led him to become the Deathless Prophet and build a religion around the artifact.

The Remnants & the people of Kitezh believe that the Divine Source holds a fragment of the soul of the Abrahamic God Yahweh, and believe that is the reason why the Divine Source is able to give immortality, but in actuality its true origins and who created it are entirely unknown. The Divine Source removes and stores the soul of whomever gazes at it, thus making them immortal. Though all of the Prophet's followers, Trinity, the Remnants and Lara Croft believed it to be Divine, only Jacob (The Prophet) knew that it was not truly divine.

Discovery by Jacob
Jacob found the artifact in 866 on the island of Rügen, near modern day Germany, among altar stones and ancient megaliths. Gazing into it, he gained immortality as well as healing abilities. He then used his new found supernatural powers to perform "healing miracles" upon people with ailments or who were close to death's door. The people soon started to believe him to be a prophet of the Abrahamic God Yahweh and the Divine Source to be of divine origin, although Jacob himself however privately knew the artifact was not divine.

Prophet of Constantinople
Word spread about the Prophet of Constantinople and the Divine Source. Trinity soon gained word and were interested in the artifact. They ordered the Prophet to be executed and the Divine Source to be acquired for themselves.

Trinity and the Prophet's pilgrims soon battled for the artifact, with Trinity killing the Prophet in the process. But despite the Prophet's death, his followers managed to acquire his body and secure the Divine Source as they fled from Trinity. The Prophet's followers built him a giant tomb in Syria. But before they could complete their work, the Prophet was revived with all of his wounds regenerated.

Exodus from Syria and Building the City of Kitezh
The Prophet and his followers soon fled from Syria with Trinity, who had learned of his rebirth, hot on their tail. After a long journey, they arrived in Siberia and stopped near a massive natural rock formation, which they took as a sign of their god. They soon settled around the valleys and even built a temple near the rock formation in order to honor the scout who discovered it.

The Prophet soon recruited the best architects, philosophers, warriors, scientists, artists, builders and craftsmen of the Byzantine Era to built the city of Kitezh. After Kitezh was built, the Divine Source was hidden and locked away in the Chamber of Souls, which is a large vault in the middle of the city. The Atlas was crafted to show its location.

Mongolian Invasion and the Destruction of Kitezh
During the Mongol attack on Kitezh, Jacob in a turn of desperation, used the Divine Source to give immortality and superhuman physical abilities to thousands of his Elite Guardians and they became known as the Athanatoi, the Deathless Ones who, alongside the people of Kitezh, fought and battled the Mongolian Invaders. Despite the supernatural advantages that the Divine Source had given them, the Deathless were still unable to completely repel the Mongol horde due to their overwhelming numbers. Knowing that they would eventually lose and desperate to keep the Source out of the enemies hands, the Deathless turned their trebuchets at the large glacier above Kitezh, bringing tons of ice down on the city. This act not only destroyed the Mongolian Invaders, but also buried Kitezh and most of its inhabitants under the glacier to secure the Divine Source.

The Prophet soon escaped the ruined Kitezh and rendezvoused with the very few other citizens who escaped the destruction, as well as those that lived outside the main city. These people start calling themselves The Remnants, who believe that guarding the Divine Source is a duty that they must pass down to their descendants. Using their Byzantine heritage, they developed tactics, weapon and combat skills which helped them survive for centuries largely undisturbed by outsiders.

Lara's search for Immortality
The legend of Kitezh and the Divine Source lived on throughout the ages, which eventually led Richard Croft to research the lost city during his search for immortality. However, he was killed by Trinity before he ever got the chance to find Kitezh.

Using his research, his daughter Lara continued the search for the Divine Source, which eventually led to her discovering the location of the ruined city in Siberia. Unfortunately, Trinity stole her fathers research and was able to decipher the location of the city as well, leading them to arrive at Siberia first where they began capturing and ruthlessly questioning the Remnants about the artifact, including Jacob. Lara herself arrived a few days afterward and immediately began sabotaging Trinity's efforts to find the Source. Though initially cautious, the Remnant welcomed Lara as an ally after she rescued Jacob in the process of escaping prison.

Lara continuously aided the Remnants in order to earn their trust and find out more about the Divine Source, though they still kept it a secret from her. However, after witnessing Jacob magically heal Jonah's wound, Lara realised that he was the Deathless Prophet, the same man who brought the Source to Constantinople and founded Kitezh over a thousand years ago. Jacob then privately admitted to her that he simply found the artifact long ago and lied about it being divine, but it was every bit as powerful as the legends surrounding it portrayed it to be. Agreeing that the risk of Trinity acquiring the Source was too high, Jacob then let Lara into the Path of the Deathless, a secret entrance into the outskirts of the buried city that would give her a chance to secure the artifact first.

Destruction of the Divine Source
Brute forcing their way through the glacier, Trinity met the Deathless Ones in open battle in the ruins of Kitezh. Despite the fact that Trinity's army were quickly slaughtered by the ancient Deathless Army and Lara with the Remnants, their hunt for the Divine Source was a success, as the main bulk of Trinity's forces managed to distract the ancient immortal guardians long enough for Ana to reach the artifact first. Lara arrived soon after, finding Ana holding the artifact. Knowing that Lara's intention was to destroy the Source, Ana pleaded with her to reconsider, admitting she had no intention of handing the artifact over to Trinity, since she just wanted to use it to make herself immortal and didn't care about their cause. She also pointed out that her father would forever go down in history as lunatic and a fraud if she destroyed the artifact. However, Lara refused change her mind about destroying the Source, arguing that death was a part of life and that she was willing to sacrifice her fathers reputation in order to keep the world safe.

Their conversation was interrupted when a lone Trinity enforcer rushes into the chamber and informs Ana that all of their soldiers have been slaughtered by the Deathless Ones, before he is quickly killed by Jacob who was following behind him. Ana quickly retaliated by shooting him in the chest. Injured, Jacob also pleaded with her to give up the Source, claiming it was not meant for the world.

Seeing that the Deathless were cautiously closing in around them Ana tries to use the artifact to make herslef immortal, by tearing off the protective gold veil covering it and staring into the bright blue crystal. However, as the artifact began to absorb Ana's soul, it nearly made her fall unconscious which caused her to drop the artifact. Lara quickly picked it up, purposely looking away from it so as to not have her soul absorbed. Sharing a silent look with Jacob, he gave her his blessing and permission to destroy it. Lara then violently threw the Source to the ground, shattering it and releasing all the souls stored in it into the air where they eventually faded away. Though this caused the Deathless Ones to immediately and violently turn to ash, Jacob was disintegrating slowly. He complimented Lara as being one of the most extraordinary people he's met in his long lifetime and assured her that she'd made difference in the world with her actions, before peacefully turning to dust.

Trinity's Attempts Salvage the Divine Source
After the Divine Source was destroyed, Trinity attempted to try and find another way to harness the power of the Divine Source, which they linked to the isle of Yamatai and the Sun Queen Himiko, who they believed still resided trapped in the body of Samantha Nishimura, they purchased the facility that Sam was being kept, and began to experiment on her. This caused Himiko to emerge and take control of Sam's body. Now free, Himiko escaped the facility to get back to Yamatai in order to ascend the throne once more, rampaging across Europe in the process.

Powers
The Divine Source was ancient, mysterious and very powerful artifact. It was able to absorb souls and through that give immortality.
 * Soul Containment: It has the ability to absorb the soul of anyone who gazes at it and store it within itself. With the soul being prevented from moving on to the afterlife, the physical individual becomes immune to a permanent death. However destroying it will release all the stored souls and in return, which in turn returns people's mortality. Should someone have lived beyond a human lifespan, they end up aging into dust. This is evident as how Jacob and the Deathless Ones age to dust, due to being centuries old, while Ana, who was also exposed to the artifact, did not turn to dust.
 * Immortality Bestowal: Because the soul of individuals who gave on the Divine Source is imprisoned inside the artifact, those individuals cannot truly die since their souls are unable to pass on to the afterlife. They also stop aging after their souls are taken from them. As long as the someone's soul is contained within the Divine Source, they cannot age or truly die by any means unless the Source itself is destroyed.
 * Regeneration/Healing: The Source greatly enhances the natural regeneration of those who store their soul inside it, as well as granting the ability to heal the wounds of others. This is evidenced when Jacob quickly recovered from a gunshot wound to the abdomen and completely healed Jonah's knife wound by simply covering it with his hand, saving him from death.
 * Physical Enhancements: On top of bestowing all of the above powers, the Divine Source also greatly enhances the physical durability and strength of individuals, as evidenced by the Deathless Ones, who were capable of taking far more damage than modern Trinity soldiers, could effortlessly lift a person up with only one hand and quickly scale a cathedral despite being in very thick full battle-armour.

Trivia

 * Jacob is apparently the only person known to have shown his humanity after gazing upon the Divine Source. However, the Deathless are not completely devoid of emotion or individuality as evidenced through an old Trinity agents notes. Furthermore, there is no mentioning of the Divine Source stripping people of humanity beyond Jacob’s own assumption.
 * Adding to this, what humanity means differs from person to person and unless the Divine Source is alive and has an agenda of its own it does not make sense for it to have a view on what humanity as a concept/ideal is, nor does it make sense for an entire army to be stripped of it, yet one person isn't.
 * Even though Trinity thought there is a connection between Himiko and Divine Source, the only similarity between them seems to be the blue light.