Sanghelios

Sanghelios is the homeworld of the Sangheili, and was one of the most influential worlds in the Holy Ecumene.

Prehistory
It has been surmised from both ubiquitous Sangheili myths and the evidence of a long-term Forerunner presence on Sanghelios and the Urs system that the Sangheili were once a Forerunner client species employed by the ecumene. During this time, the Forerunners built various artifacts on and around the planet, most prominently what the Sangheili would later come to call the Shard of Heaven: a large space station evidently serving as a defense system against incoming asteroids and space debris, as well as potential enemies without and within. During this time, the Sangheili enjoyed access to spaceflight through their client status, largely using "black box" technologies provided to them by their overlords; as with many cultures the Forerunners took under their guardianship, this also disincentivized native technological development, making the Sangheili reliant on their masters.

Primeval Period
After their reseeding following the firing of the Halo Array, the Sangheili led a paleolithic-equivalent pastoralist existence, until the gradual development of advanced agriculture brought on the first large civilizations. The preindustrial era since the local bronze age was a time of great heroes and legends, as the Sangheili slowly conquered the planet's hostile seas and unforgiving deserts, sailing to previously-undiscovered continents and fighting wars with newly-encountered civilizations, with great empires having thrived in sheltered mountain valleys and jungles or faraway islands.

Several of the continents on Sanghelios have weather cycles measured in hundreds or thousands of years, and are only intermittently fertile. Empires rise up in the fertile intervals, only to collapse and retreat into narrow river valleys as the rains dry up. One such civilization (the People of the Sea) was the first to master ocean navigation and wind power, and for several centuries they traded with bronze-age civilizations on a neighboring continent, civilizations which were fairly uninterested in exploring the ocean themselves until the People of the Sea up and vanished in the span of a single generation.

First civilization and downfall
Circa the 3rd millennium BCE, Sanghelios enjoyed an age of unprecedented technological advancement and societal progress. Gleaming megacities supported a planetary vast population, with a growing number of Sangheili living in orbital habitats and even a handful of off-world colonies. This period, known as the Age of Decadence by latter-day Sangheili, was brought to a screaming halt around 2,300 BCE. Although records of what exactly happened are now lost to history, some sort of experiment caused the Shard of Heaven to malfunction. This triggered the Skyfall: the early orbitals of Sanghelios were wrecked and came crashing down on the surface, and most higher forms of technology ceased to work. Millions were killed in the first day alone, and far more perished in the days, weeks, and months, as the disaster expanded in scope with the collision of asteroids and comets previously held in place. To say that the Sangheilian disaster-relief procedures could not cope was a significant understatement. They had been reduced back to a pre-space age civilization, and their colonies throughout the system were forced to fend for themselves. Without support from Sanghelios, most of the smaller outposts died out, with significant populations maintained only in the best-established colonies.

Though the Sangheili eventually recovered, the Sangheili were permanently affected by the event. Not only did it showcase the power that inert Forerunner god-machines held, but it also saw the disappearance of their most holy artifact. With their belief in science shattered and so much trauma inflicted, many turned back to religion to cope, in particular one belonging to a state that had always opposed reliquary experimentation. By the time the Sangheili returned to space so many centuries later, it was with a conservative, deeply-traditional culture.

New space age and founding of the Covenant

 * Many states' union against the Dominion of Nar'segha - saw the formation of the first Swords of Sanghelios
 * Pre-Covenant Sanghelios was a lot like Earth in terms of factionalism; Had two-four major power blocs after the redevelopment of civilization, but a couple of these were very diffuse rather than unitary states. At the time of the War of Beginnings, these included the Crimson League, the Thar'shi Sphere, the Irshun League, the Daikasem Convention, and the Khaaton Realms. Crimson League and Thar'shi were the big players on Sanghelios
 * Most countries operated on pseudo-feudal structures (though more cohesive states / empires have existed throughout history - this is cyclic), but much more politically-complex than today.
 * Some had off-world colonies, but relationships were loose and there have been plenty of wars (nothing like the Insurrection though!). Some multi-colonial states were extensions of states on Sanghelios.
 * Off-world colonies began to diverge considerably from Sanghelian culture. Arbiters attempted to bring them back into the fold, though there were far too many and were far too different to bring them back under military force.

Covenant history

 * Sanghelios/Urs was the Covenant capital before High Charity
 * The Covenant's adoption of Sanghelios' institutions saw its culture become hegemonic in the rest of the Covenant sphere
 * Had lengthy periods where High Charity docked at Sanghelios between tours of the Covenant Sphere.

Years of Disquiet

 * Had trouble controlling fractured Sangheili polities beyond the Sunlit Worlds.
 * State of Vadam elects a new Kaidon in Thel's place - Thel does not pursue it, though there is considerable tension between the two. Vadam probably declines a bit due to the shame, because of politics, and because he's very busy with running the Concord.

Tribulations and Blooding Years
Between the 2560s and the 2590s, Sanghelios has gone through a period of turmoil with internal forces seeking to break the Swords of Sanghelios' hold over the planet. The Sunaion Uprising perpetrated by the Watchers of Heaven in the late 2570s began a conflict known locally as the "Crimson War".

Physical characteristics

 * Sanghelios is denser than Earth and iron-rich, and iron oxides in the crust give the planet its rust-red color
 * Suban formed as a result of a protoplanet collision with primordial Sanghelios and is mostly made of the same stuff
 * A hot and harsh world overall; the equatorial belt is uncomfortably hot, and mostly desertified; civilization clusters toward both poles; in earlier history, crossing the equatorial wastes or the ocean there was a great undertaking; though hardy wanderer-tribes survived in the deserts. Still has some ice in the poles and highlands.
 * Has five continents, all of which are more scattered compared to Earth
 * Apparently has 0.9 atmospheres of pressure at sea level, which is odd - can be tweaked
 * Planet's water has various hues - blood red, orange, yellow, cyan, blue and even purple or magenta (suggesting the seas are shallow, with the reddish rock being visible underneath)
 * Continental interiors mainly composed of deserts
 * Very strong tides due to the moons + lots of inclement weather, big storms
 * Most of the population live on the coast or islands - preferred locations are those ringed by mountain ranges or rocky tombolo drifts. Like on Earth, civilization first developed in fertile river valleys/canyons, even caverns?
 * Axial tilt and seasonal cycle? Has a very bad rain season (though likely contained to given areas of the planet)
 * Some meteorite impacts from Suban have brought blamite to the surface.
 * Industrialization during Sanghelios' prehistoric habitation has made the planet relatively poor in readily-accessible fossil fuels. Though oil, natural gas, and coal can be found on the world, the Sangheili would also use methane hydrates trapped in the seafloors fairly early on to fuel their growing industry. Nuclear, wind and photovoltaic power were also developed relatively early on, with both wind and sunlight being abundant, and fissile material reasonably so.

Ecology
On Sanghelios, the evolutionary transition from the oceans to land-based life happened relatively quickly due to the frequent flooding of coastal areas, thanks to the planet's high tides. Pseudo-reptilians such as Sangheili are the planet's dominant form of fauna, though other categories (such as mammaloid, insectoid, piscine, and mollusc-like species) exist. The Sangheili's unique quad mandible structure is shared by their entire taxonomic order, though the exact shape these take in different families and genera of species has diverged over time.

A large portion of the plant life on Sanghelios uses retinaldehyde as its photosynthetic pigment rather than chlorophyll, making purple, rather than green, the predominant color of plant life. Although chlorophyll is more common on worlds with complex life, Sanghelios is not unique in this, and purple flora has evolved independently in several biospheres outside that of Sanghelios. As a result, purple and pink shades functioned perfectly as camouflage, along with the red-orange commonly found in Sanghelios soil.

Flora and fauna native to Sanghelios appears to have been transplanted to other worlds in ancient times, resulting in several worlds in the Covenant Sphere housing out-of-place biota descending from Sanghelios life.

Government and politics
Governments and polities on a global scale have been quite rare throughout the planet's history. Those that have, have mostly come about in response to external developments. During the War of Beginnings for example, the polities of the Righteous Host alliance de facto controlled a huge swath of the planet. More recently, the Sanghelios Plenary Council and their replacement, the Swords of Sanghelios, have also both operated nearly across the whole planet. Though as of the late 2570s, the Swords have had their authority challenged internally.

Culture and society
Although forms of Forerunner worship have always been commonplace on Sanghelios, ancient Sangheili religions varied. Some of the preindustrial Sangheili religions were based around a pantheon of gods. One of the largest or most enduring faiths worshiped the system's stars, particularly Urs, as divine. While not practiced worldwide, this faith had a longstanding cultural impact that resonates even in the present day, long after being replaced by the worship of the Forerunners.

Ground locations

 * Kaepra
 * Bdaoro City
 * Sunaion
 * Yermo
 * State of Vadam
 * Kolaar Mountain

Satellites
Sanghelios is encircled at the equator by an orbital ring known as the Silver Girdle. This complex of facilities, which dates back to the Covenant's late antiquity, houses many of the planet's orbital ports, spacedocks and shipyards, along with a number of planetary defenses. Numerous gravitic sky-lifts link to the structure from the surface. Other than the Silver Girdle, Sanghelios is surrounded by a swarm of stations both civilian and military.

It is commonly deduced based on ancient records and even folklore that Sanghelios once had at least two more minor satellites, which were mined out in their early days of space travel.

Suban
Suban is the larger of Sanghelios' two natural satellites and orbits relatively close to the planet. An arid moon, Suban has been a historically important location for the Sangheili.

Qikost
A moon largely covered in oceans, Qikost is a notable aquacultural site for the Sangheili and home to various population centers. Its oceans have served as a major source of deuterium for fusion purposes since the Sangheili's early spacefaring days. Although smaller than Suban, Qikost is nonetheless fairly large and has considerable tidal interactions with Sanghelios.