In the mid-23rd century, Cestus III was on the frontier of Federation space, in a region bordering the territory of the United Federation of Planets and Gorn Hegemony, and near space claimed by the Metrons. A century later, this planet was considered to be "on the other side of the Federation" from Deep Space 9, approximately two weeks from the Bajoran system by subspace message and eight weeks at the SS Xhosa's maximum warp. (TOS: "Arena"; DS9: "Family Business", "The Way of the Warrior")
In a commercial for Tribbles cereal, Cestus was shown on a computer screen of a food synthesizer in the mess hall of the USS Ravenous. It was listed along with other locations such as Earth, Vulcan, Izar, Andoria, Tellar, Rigel VI, and Rigel X. (ST: "The Trouble with Edward", credit cookie)
In 2267, an Earth observation post was commanded by Commodore Travers. The establishment of this colony alarmed the Gorn Hegemony; they regarded Cestus as part of their space and the colonists as invaders.
That same year, a Gorn captain led his starship and ground forces in a counter-invasion strike, destroying the colony and killing many of the colonists. Using faked communication and impersonating Travers, the Gorn lured the USS Enterprise to Cestus III, where the landing party, led by Captain James T. Kirk, beamed down to the planet's surface. After the surface forces were repelled, thirty medical personnel were beamed to the planet on a search and rescue mission for additional survivors. The Enterprise pursued the Gorn vessel to a point near 2466 PM, where both ships were seized by the Metrons and their captains forced to do battle on a nearby planet prepared for them by the Metron. (TOS: "Arena")
Kirk's confrontation with the Gorn would later become one of the most famous incidents in his career. Benjamin Sisko admitted he'd like to shake Kirk's hand and "ask him about fighting the Gorn on Cestus III." (DS9: "Trials and Tribble-ations")
In 2371, the colonists formed a baseball league with six teams, including the Cestus Comets and the Pike City Pioneers. Kasidy Yates's youngest brother lived on Cestus III and invited Sisko and his sister to see a live baseball game at the colony in 2372. (DS9: "Family Business", "The Way of the Warrior")
"SES-tus" was the pronunciation for this planet's name from the script pronunciation guide for "Family Business".
In the final draft script of "Arena", the Cestus III outpost that appeared in that episode was initially described thus; "This is a military-scientific outpost of the Earth Federation... a limited number of facilities on the surface, most of it below ground. But what we see [...] is smoking ruin... desolation. Cestus Three, in terms of structures and settlement, no longer exists. It has been smashed. All that we see are ruins with here and there a silent body lying dead." The script further established that the destruction included all of the outpost's underground section and that the Human population of the outpost was listed as five hundred twelve at the time of the Gorn attack.
The remains of the Cestus III outpost was actually a fort constructed for a film about the Alamo in the 1930s. It was believed to be unsafe and was demolished in the late 1960s. (Star Trek Encyclopedia (4th ed., vol. 1, p. 128)) Directional signs for sections of the outpost were posted on the interior walls of the fort. There were signs for the Material Department, Life Support, Residential Area, and Engineering Section.
For the 2006 "remastered" version of "Arena", a new, computer-generated version of Cestus III, as seen from orbit, was created to replace the grainy, undetailed globe in the original edition. A new matte painting of the outpost was also created, showing more damage and more detail in the surrounding terrain. This version was displayed above.
According to Star Trek: Star Charts (p. 52), an Earth colony was first founded on the class M planet Cestus III in 2265. Under the terms of a treaty ratified in the late-2260s, Cestus III would be resettled and shared by both Humans and Gorn. In 2271, the colony was resettled and, later that year, was admitted into the Federation. The capital city of this planet was Pike City. The two dominant species of this planet were the Humans and the Gorn. In 2378, there were 28.6 million Humans and 7.2 million Gorn living on this planet.
According to Star Trek: Star Charts (pp. 57, 64, "United Federation of Planets II") and the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Cestus system was located in the Beta Quadrant. The primary was an A-class star. In the late 24th century, this Federation system was a destination on a major space lane.
The Pocket TNG novel Requiem, by Michael Jan Friedman, depicted a time travel scenario in which Captain Jean-Luc Picard was transported back in time to Cestus III, shortly before Commodore Travers' outpost was destroyed.
Nanietta Bacco, who was sworn in as Federation President in Articles of the Federation and served during the Destiny series, hails from Cestus III, and had been Cestus' governor before winning the Presidency in a special election just prior to the Shinzon incident.
According to the novel Seize the Fire, the Gorn name for Cestus III was "Inner Eliar".