It has its own Uyseʔic language, Siadese, closely related to Uyseʔ. (The aspirates of Uyseʔ become fricatives in Siadese; thus the β in the name of the country.) Its people are, like the Uytainese, of the Adurise race.
Agriculture spread to the Yurdzo valley by 600, with the same crops and techniques as in Uytai. Very likely the spread was along the upper Hurtso, not along the coast, and involved both migration and local adoption.
The establishment of the kingdom is the work of Hendwor; in legend this was an epic war, but in fact it largely consisted of overcoming the resistance of Púempo upriver. Nonetheless the creation of state-level authority was an achievement. His son Swarγuy organized the rebuilding of Ɣardze according to the grandiose plans of his architect Faegroy, who outlined a city plan larger than that of Uykhrai, and created wide boulevards and empty estates with walls that made the town look much larger than it really was.
The country expanded to fill the Yurdzo watershed, and came to adjoin Uytai in the west. Though this led to occasional wars, the country was considered too remote and resource-poor to conquer. Culturally, the Siadese fairly slavishly copied the government of Uytai and its innovations, such as the writing system.
The northern half of the country was briefly occupied by Krwŋese refugees after the ecological collapse of Krwŋ in the 1600s.
In 1937 Nyekhrai, emperor of Uytai, put his nation’s new mastery of iron to good use by invading and conquering Siad βo. He had acquired an enormous steam catapult from the elcari and used it to attack the gates of Ɣardze— where it broke down, and was left there. It was still visible centuries later, and gave its name to a later suburb, Catapult Hill.
The Sumë warlord Ga-Tlan, son of Tlan, conquered the country in the early 2000s, but the Siadese rebelled and killed him in 2012; as the Sumë continued to harass Uytai this was enough to reestablish Siadese independence.
In the 2300s the Gleŋ occupied the northern half of the country, and in 2531 the southern portion was taken over from an unexpected direction, by Ťrim. This was not entirely unwelcome, as the Gleŋ were notoriously oppressive rulers. The Siadese pushed the Gleŋ out of the country in the 2600s, with Ťrimese help; but actual Ťrimese administration was now seen as anachronistic, and the Siadese negotiated their independence in 2695 under king Niurkian.
The Uytainese were now under the dictatorship of the Patriots (ħwentai), and many Uytainese had fled to Siad βo; this was a constant bone of contention. When king Mampao was pushing the Ōkmisan out of its northern territories, it led to conflict and then war along the Hurtso.
The Siadese posed as liberators, restoring the Yonram or Uytainese legislature and local authorities deposed by the Patriots... freedoms not granted back home, where Mampao ruled absolutely. This was at least partly successful; the Uytainese didn’t fight very strongly for the Patriot regime. More importantly, Mampao had secured Verdurian military assistance. He advanced along the Hurtso, taking Tsopwan in 3358, the coast by 3362, and Uykhrai in 3365. They were unable to take Srethun, and Uytainese rebellions held power in Phetai and in the northern highlands, but Siad βo now held the bulk of Uytai.
This was a strange upending of tradition, and the Siadese did their best to be helpful and respectful, helping to lead the great nation of Uytai into the modern world— for instance, setting up an academy in Thestyet, the Taiħwul, which taught Uytainese and Siadese history as well as Verdurian and modern science. The Uytainese reacted with predictable annoyance to this condescension from a nation still considered barely more civilized than the Ōkmisan.
[[Image:Uytai-girl.png|thumb|250px|right|Hiefae, leading scholar of Siad βo The Uytainese in the north, the Restoration, moved southward, taking Uykhrai in 3414, and the Patriot enclave in Srethun in 3420, and finally took the delta and Tsopwan by 3438. The Siadese were however left with half the Hurtso, including the city of Raumnye.
The country remains backwards in many ways; it is still not as urbanized or prosperous as Uytai. At the same time, it understands the threats and opportunities posed by the Ereláeans better than the Uytainese, whose long cultural and military predominance has led to complacency. Siadese intellectuals, led by the female scholar Hiefae, have vigorously questioned antiquated notions and sought to learn from Ereláe without denying Arcélian civilization.