After the tragic death of his formal rival and friend Enkidu, king of Uruk Gilgamesh set forth on his quest to find the secret to eternal life so that he would never face his own dark end. He journeyed to the end of the world, traveled underground through a tunnel under Mount Mashu, crossed the oceanic Waters of Death, and at last met Utnapishtim, an immortal man who survived the Great Flood centuries before. Utnapishtim admited that his immortality was singularly bestowed from the gods, not something that can be replicated. Saddened, Gilgamesh prepared to leave.
He was granted a final token, however: the story of an undersea plant that granted eternal youth. Gilgamesh dove for the flowering plant called Ur-shanabi, the "Plant of Heartbeat," with rocks tied to his feet. Despite it being covered in thorns, he seized it and began the long journey back to Uruk. Along the way, he was tempted to bathe in a glistening pond to prepare for his reentry to the city, but a prickle of a thorn prompted him to be determined in keeping his precious plant safe. He even slayed a serpent wandering nearby out of caution.
Gilgamesh's experiment of giving some of the plant to an old man in the city turned him into an eager youth once more. Gilgamesh then used the plant himself, maintaining youth as he built a grand garden centered upon it. Word of the plant spread through the ancient world, causing many kings to seek it for themselves. Gilgamesh proved selfish with eternal youth, granting it only to those who proved themselves worthy and humble before him and the gods. Those sentenced to die routinely besieged the city, but Uruk's walls and Gilgamesh's semi-divine strength proved too strong. The Pharaohs of Egypt, unable to seize the flower, cursed it as sacrilege against the cycle of death.
Gilgamesh ruled for over 1,000 years, keeping at bay opponents even as powerful as the Assyrians, until the Hittites came with their iron chariots. He fled with the plant, although cuttings were delivered to the Hittite kings, who established their own rule over the Middle East. Although the plants established a ruling class of century-lived royals, climatic shift brought an era of drought to the region. The starving populace rebelled against their kings, many of them who had established themselves as gods on Earth now seen as powerless. The resulting dark age eventually brightened as Babylonians again established rule, only to be eclipsed by the Medes and Persians. They themselves were conquered by Alexander, leading the Greeks.
When Alexander fell ill in Babylon, a mysterious visitor arrived at court offering the curative properties of a thorny plant. He was physically young and enormously strong, but his eyes were wizened by uncounted centuries. Although the interpreter struggled to determine the man's accent, the man's royal stature prompted Alexander's guards to allow him to pass. The man introduced himself as "Gilgamesh" and said that a plant he offered would cure any illness and return Alexander to his youthful vigor. He had made his offer to Cyrus the Great, but Cyrus had refused, stating that eternal youth would only make him weak in his day-to-day affairs.
Alexander, however, leaped at the chance. Upon his recovery, Alexander placed Gilgamesh as ruler over conquered Babylon, just upriver from the ruins of Uruk. Alexander himself marched west, ultimately reminding the world that eternal youth was not immortality when his life ended upon a Roman blade.
Gilgamesh continued his rule. Rather than holding his plant selfishly, he sent envoys to rulers he deemed suitable bearing a flowered gift worth another lifespan. His kingdom remained strong, although it faced increasing strife from the west and south as monotheists stated that God demanded death from men. Waves of crusades and holy wars marched against Gilgamesh, but he was aptly supported by his allies in the east, including the Great Khan, who would rule the greatest empire on Earth for centuries.
Despite the European kings decrying the flower, it gradually became proven that many of them secretly bought their own clippings and replaced their own sons upon tasting its gift of youth. Sciences of botany and chemistry progressed as scientists attempted to unravel the secrets of enzymes within the plant. When at last a synthetic Formula of Life was created, the growing middle class of bankers and merchants proved a fertile ground for sales. The widespread interest was met with large-scale production in the Industrial Revolution, and soon Earth faced a new problem of rampant overpopulation of ever-young, healthy citizens clamoring for resources.
Gilgamesh himself continued to rule over a carefully cultivated Mesopotamia, the one center of progress and peace on the world, surrounded by enormous walls to keep out anyone deemed unworthy.
In reality, according to the Epic of Gilgamesh, the oldest recorded literary work, Gilgamesh lost the plant to the serpent as he bathed. He returned empty-handed to Uruk, where he took great solace in seeing his works, such as the great walls of Uruk he erected to defend the city.