Hadrian is a human system in the galactic south along the Arachnid Quarantine Zone. It was taken from the Bugs in the early 2020's by the Tech Infantry, and is one of several ex-Bug systems in the area named for ancient Roman emperors. Its Impball team is the Hadrian Vampires.
Hadrian is unusual in having two inhabited worlds. The first, the planet Hadrian itself, is a large rocky world with a dense, hot, wet atmosphere, large oceans, and expansive forest and swamp areas. Its high gravity limits settlement and growth potential, but it does grow some of the strongest and densest lumber in known space, which is in high demand for custom furniture.
The second inhabited world is New Sparta, a moon of a gas giant a little further out from the star. New Sparta is a small windswept moon with an extreme axial tilt of almost ninety degrees, giving it the greatest seasonal variation of any human-settled world. Part of the atmosphere actually freezes solid at the dark pole during the long winters, and then boils away in the extreme heat of the following summer. Along the equator there is a habitable belt of flat steppes and mountains covered in forests of Terraforming Pines. Temperatures here are generally bearable, although the extreme winds caused by air flowing from the hot high-pressure area around the sunlit pole to the cold low-pressure area around the dark pole cause extreme weather every summer and winter. Springtime and Autumn are quite lovely, however. Within this habitable belt, eccentric billionaire Izzy D'Argent has built an enormous amusement park known as Sylvania.
Posession of the Hadrian system has gone back and forth many times during it's history due to its location at the crossroads of several different factions.
A few years after the Earth Federation bagan colonizing Hadrain, the Second Civil War prompted may border systems, including Hadrian, to break away from the Federation and form the Frontier Worlds Territory instead. During the Third Civil War twenty years later, New Sparta was briefly the home in the early 2240's of Project Bolo, a joint research project between the Federation and the Frontier Worlds Territory. The research facility survived a Bug raid, but was then destroyed by a sneak attack by Horadrim warships on behalf of Andrea Treschi and his new allies in the Internal Security service... for reasons that have never been adequately explained.
In the later stages of the Third Civil War in 2243, a joint assault of the K'Nes and Jurvain overran and conquered the Frontier Worlds Territory. Facing imminent invasion, the governor of Hadrian asked for protection from the Eastern Bloc, which reluctantly agreed and sent in a small fleet to defend the system. This essentially amounted to an uncontested de facto occupation of Hadrian by the Eastern Bloc, and the system was ceded to them in the Treaty of Wilke's Star which ended the Third Civil War the following year.
Since the Frontier Worlds Territory had never actually been at war with the Eastern Bloc, and Hadrian had joined the Bloc voluntarily, the colonists received much better treatment than other Federation worlds the Eastern Bloc had conquered during the later stages of the Third Civil War. Although the non-han Hadrianites were still treated as second-class citizens, so long as they paid their taxes and obeyed Bloc laws, they were granted a limited degree of Home Rule and pretty much left alone to govern themselves.
Eight years later, the Eastern Bloc was all but wiped out by the Vin Shriak invasion of 2251. Although Hadrian suffered a few raids during the Vin Shriak Holy War, the colony was largely considered too small and strategically unimportant for a major assault, and managed to survive the war more or less intact. When the Earth Federation finally defeated the Vin Shriak in 2255, Hadrian happily rejoined the Federation. In the ten years of relative peace that followed, Izzy D'Argent built Sylvania on New Sparta in an attempted to stimulate the Hadrian economy with tourism revenue.
In 2264, the path of the Caal Invasion narrowly avoided Hadrian. This invasion triggered the collapse of the Federation, and In the chaos that followed, Hadrian joined the newly-formed Terran Republic, mainly for mutual protection against the Bugs. Early in the Ascension War with the Holy Terran Empire, the Imperial Navy sent a probing attack into the system, but Hadrian's substantial orbital defense network (designed to combat a Bug onslaught) inflicted sufficient damage for the Imperial warships to withdraw. The Empire consequently decided to launch its invasion of the Terran Republic from the Wolf system instead, and Hadrian saw no more fighting during the war. With the destruction of the Terran Navy at the Battle of Epsilon, the Terran Republic collapsed and Hadrian was absorbed into the Empire.