From Halopedia, the Halo wiki
Sunaion, also known as the Westward Temple of the Sea, is a Sangheili city on the continent of Qivro on Sanghelios. It is situated above the Csurdon Sea and features large desalination devices used to remove minerals from the saline water.
When a Forerunner Guardian was discovered in the Csurdon Sea by dive-hunters and fishing skiffs, ancient Sangheili elders established stone fortresses along the Nuusra coastlines to observe and protect the immense construct that they deemed sacred. Centuries later, Sunaion was built as a temple city over the water near the Guardian, as the Sangheili recognized that the construct belonged to their gods, the Forerunners.
When the Covenant was established, the empire initially used Sunaion as an operating base while they explored and worshiped the Guardian. Despite the Covenant's efforts, little could be done to explore the construct nor could they determine its true purpose. During most of the Covenant's rule on Sanghelios, Sunaion remained largely empty, even during the Human-Covenant War. After the Covenant War and the empire's fall, Sunaion remained largely neutral in the resulting civil war that engulfed much of Sanghelios.
By 2558, Sunaion became viewed as an optimal staging point by kaidons seeking to overthrow Arbiter Thel 'Vadam and his Swords of Sanghelios; the city allowed quick access to the shores of Yermo that led to the state of Vadam. After the death of Jul' Mdama, his Covenant attacked Sanghelios, took control of Sunaion and began formulating plans to invade Vadam. The Arbiter learned of the Covenant's intents and quickly established a forward operating base in the ruins of Nuusra, where the Swords of Sanghelios prepared to attack Sunaion. Soon, an engagement between the joint forces of the Swords of Sanghelios, the United Nations Space Command and Jul 'Mdama's Covenant. Fireteam Osiris, led by Jameson Locke, took part in the operation and aided the Swords against the Covenant's forces. Sunaion was considered the last stronghold of Jul 'Mdama's Covenant on Sanghelios and was where the last of the Covenant fell in battle.
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