Battle of Sanghelios

At the end of the War of Beginnings, a major battle on Sanghelios took place between the San'Shyuum Reformists and the Sangheili. It occurred in the Urs system, specifically on the Sangheili homeworld of Sanghelios and its two moons, Qikost and Suban. Ultimately, the battle would end with the San'Shyuum and Sangheili forging a tenuous truce, formalized with the Writ of Union, which birthed the alliance known as the Covenant.

Background
The War of Beginnings had been sparked when the San'Shyuum first arrived on the Sangheili colony of Ulgethon in 938 BCE. While the two species' first encounter went well, it was soon revealed that the San'Shyuum planned to excavate the world's Forerunner artifacts. The Sangheili, who also worshipped the Forerunners, saw such manipulation of their gods' relics as blasphemy punishable by death. As such, Arbiter Vema 'Togad executed a San'Shyuum delegation, an action which led to the destruction of Ulgethon, the first battle of a decades-long war between the two species.

However, as the war raged on and colony after colony was lost to the San'Shyuum's powerful Keyship, Anodyne Spirit, the Sangheili would eventually amend their stance on the use of their gods' technology. The discovery that the Sangheili had likewise begun to make use of Forerunner weapons softened most San'Shyuum toward the possibility of a cease-fire, but Pervading Stone, their leader, only grew more incensed. Some other respected San'Shyuum, such as Breaking Shadow and Ushering Dusk spoke out against him, but were unsuccessful. The act of beginning to reverse-engineer Forerunner technologies saw the First Kaidon of Sanghelios, Mhelaat 'Orlam, assassinated for his perceived crimes—though he was succeeded by his son, Pelahsar the Strident. Pelahsar was undeterred by his father's death, and continued to engineer a new fitted with the experimental weapons in question. The warship proved successful during testing and was named Reckless Pursuit.

War for Sanghelios
Seeking to obliterate the Sangheili once and for all, Pervading Stone finally took the Dreadnought to Sanghelios, ravaging both the planet and its moons, Qikost and Suban. During the battle, the San'Shyuum and Sangheili fought for possession of numerous Forerunner artifacts on Sanghelios. Many Sangheili city-states were assaulted as well, including the state of Vadam. However, the Vadam keep's well-defended position in Kolaar Mountain prevented it from being destroyed by the San'Shyuum. Ultimately, the Sangheili unleashed their powerful Forerunner-derived weapons on the Dreadnought with Reckless Pursuit, successfully managing to shoot it down on Suban and trap it where it landed using gravity anchors. With the San'Shyuum held captive within the keyship for some time, the Sangheili debated whether to simply destroy the vessel and those within, or to breach it and take the Dreadnought for themselves.

By 855 BCE, while the Dreadnought was still immobilized on Suban, Breaking Shadow had led a coup against Pervading Stone that resulted in his assassination. Following his death, the San'Shyuum aboard the Dreadnought were more unified than ever. Breaking Shadow prepared to finally present the possibility of peace to the Sangheili. In 852 BCE, the San'Shyuum sent an unarmed delegation to the Sangheili, who recounted all that had transpired in recent years. After this meeting, Breaking Shadow and newly-appointed First Kaidon Pelahsar the Strident forged a tenuous truce, forgiving the other's species for their crimes and working toward peace. This agreement was formalized soon after by the Writ of Union.

End of the war
The Writ of Union acted as a covenant between the two species and a formal recognition of their shared focus, the worship of the Forerunners and the exploration of their artifacts. The document was founded on the belief that despite their differences and violent history, the San'Shyuum and Sangheili could work together to purse the Sacred Rings and transcend into divinity; this was the birth of the Covenant. The Writ of Union also explicitly required both species to lay down their arms in the interest of unity. This meant that the San'Shyuum would decommission their Dreadnought, assigning it as a permanent fixture of High Charity, providing power to the holy city that would on day become the center of Covenant empire.

List of appearances

 * Halo: The Cole Protocol
 * Halo: Broken Circle