Sylvarant (シルヴァラント?), the "Declining World" (衰退世界?), is the starting world in Tales of Symphonia. It is part of the cross-dimensional world Aselia, mirrored by another world, Tethe'alla. As per tradition, there exists a Chosen who is sent to regenerate the world by making a pilgrimage to the elemental seals and, finally, the Tower of Salvation, an enormous tower that reaches to the skies when it is time for the Chosen to go on the Journey of Regeneration. Sylvarant's moon is named "Tethe'alla", and "Sylvarant" is the name of Tethe'alla's moon. In Tales of Phantasia, Aselia has two moons, both of which are named after the dimensions that were fused to create it.
Sylvarant is mostly a verdant planet abundant in trees and mountains. Its geography is comprised of four continents, albeit relatively unnamed. Its largest continent houses the Asgard region and its subsidiaries, which include Luin, Hima, the Tower of Mana, and the subcontinent of Balacruf. The Tower of Salvation also nests here when the Chosen's Journey of World Regeneration begins. The continent has two lakes: Lake Umacy and Lake Sinoa, which rests beneath Luin and splits part of the continent with a river that connects the lake to the ocean. While Hima is situated in the western part of the continent's large and only mountain chain, Asgard resides on the eastern part.
The subcontinent of Balacruf houses the Balacruf Mausoleum, a relic of the ancient Balacruf Civilization, and the Asgard Human Ranch is stationed on the northeastern portion of the continent, terrorizing nearby settlements, particularly Luin. Hakonesia Peak connects the large continent with the smaller continent attributed to Palmacosta. The Palmacosta continent is relatively empty, apart from its main city and the Palmacosta Human Ranch that lurks just behind the nearby mountains. Partially split by a small river, the continent is defined by a long trail that spills down from Hakonesia Peak. On the eastern coast lies Thoda Dock, which offers transportation to the Thoda Geyser island.
Sylvarant's southwest continent is home to the forested village of Iselia, as well as the Iselia Human Ranch hidden within Iselia Forest. The lower portion of the continent is marked by Triet Desert and its accompanying town and ruins, as well as the Renegades' Sylvarant Base. While the desert opens to its northern path to Iselia, mountains close the eastern side, and Ossa Trail cuts through the mountains to the small fishing port of Izoold. The continent's northeastern tip barely connects it with the Asgardian continent. In Sylvarant's northwestern hemisphere, a lone continent, the planet's smallest, houses only the small Katz' Village.
Sylvarant was once a country part of the world known as Aselia. Around 5,000 years prior to the events of Tales of Symphonia, a conflict known as the Kharlan War ignited between Sylvarant and another country, Tethe'alla, due to the advent of magitechnology. The war lasted for at least 1,000 years, when finally, a young boy who would later become known as Mithos the Hero successfully forged pacts with the world's Summon Spirits and ended the war with his three allies. The war, however, caused irreversible damage to the planet's World Tree, the source of the planet's mana, so Mithos used the Eternal Sword to manipulate space-time and split the planet of Aselia into the separate planets of Sylvarant and Tethe'alla.
Due to the mass depletion of mana, the two worlds became forced to vie for mana in a seesaw-oriented system of mana links. Mithos constructed a system in which the hourglass planets house an even number of Summon Spirits to correlate yet oppose the other planet's Spirits in an elemental fashion. Through this system, neither planet was able to advance too greatly in technology before succumbing to the opposing planet's accumulation of mana. This aids in deterring the reinvention of magitechnology and a return of war. In an effort to manage the balance of mana between the two worlds, a Chosen of the lesser planet embarks on the Journey of World Regeneration to unlock the seals at a series of elemental temples. The unlocking of these seals leads to the reversal of the mana links, which in turn, redistributes the flow of mana into the declining world from the more prosperous world, thereby leading to its decline while the lesser world's civilization is given the opportunity to progress forward.
The process is repeated when the flourishing planet grows too advanced technologically, and the opposing world's Chosen ventures on the regeneration journey to reverse the mana links once again. More than 800 years prior to the events of Tales of Symphonia, the Chosen Spiritua successfully managed to reverse the mana flow in favor of Sylvarant, leading to the prosperity of the Sylvarant Dynasty (シルヴァラント王朝 Shiruvaranto Ouchou?, "Sylvarantian Dynasty"). This point in history is widely considered to be Sylvarant's glory period. During the events of Tales of Symphonia, Sylvarant is in the declining state of balance of the mana flow, with its mana being fed to Tethe'alla, although evidence shows that Sylvarant has been in decline for a fairly long time due to the multiple failed Chosen following Spiritua's success. Similarly, this is the cause for Tethe'alla's significantly more advanced technology, having had centuries of development and progress due to the higher concentrations of mana.