The Casse came to Britain in an unknown year, but likely in the third or fourth wave of Celtic migrants from Gaul. They established themselves as a military and trade power swiftly. They traded with Gaul, the Greeks, and likely many others. They were very similar to Gauls in many respects, like most southern Britons, and had some influences from the Belgae as well. Archaeological evidence, and transcribed oral histories, copied in later periods by Christian monks, point to stories of a failed attempt at unifying the whole island under their rule. A plague racked the Casse and their subject tribes, among them, the Atrebates, Icenes, Trinovantes, and others. The plague was seen as a bad omen, as the king and several sub-kings had died from it, so the attempt fell apart. Caesar recongized them as the Catuvellanians, and called their king Catuvellanius, likely taken from an actual Gallic title; 'Catuvallanorix', or 'King of the Islanders'. At any given time, their power waxed and waned in varying levels of severity, but they remained some of the best organized, strongest, and most wealthy of all Britons. Their control of tin trade, large silver reserves, and substantial wheat harvests ensured them a place as the most powerful in Britain.

Culturally, the Casse were very similar to the Gauls and Belgae, with distinct Briton influences. They had advanced coinage, large mines (significantly larger than Gauls or Belgae, for that matter), quality metallurgy, and an involved political and legal system. The average person's life was spent pursuing a trade, going to a school, becoming a soldier, or going into politics, not unlike a later society. Day to day life for Britons would be a bit more stressful than it was for their Gallic counterparts; the threat of enemy tribes raiding or invading was constant. However, that doesn't mean every moment was purely war. A favored pastime was sports, including a game we now call 'hurling'; so popular was this game in all of the British Isles, that it's mentioned in numerous legends. The Irish hero Sentata, better known as Cu Chullain, was noted for his great skill in hurling. They also told lengthy stories, sang, played music, and created poetry, about such heroes, wars, and gods. They engaged in large public feasts, keeping the local chiefs and chieftans as somewhat accessible characters, to whom the people felt an honest relation. This practice encouraged a tribe to feel exemplify their relations; the extensive Celtic clan model encouraged loyalty, so long as the people felt they were truly related. They were also good farmers, and had a strain of wheat grain that was exceptionally healthy, pointing to an advanced understanding of farming methods. They also ate a great deal of meat, especially compared to later civilizations in the region, which likely accounted for their great size; they were even taller than Gauls. Swords were not as common among the Britons; iron was expensive, and often imported from Gaul or the Goidils in modern Ireland. Iron was favored, instead, for spear and javelin heads. Swords in the south were often imports from Gaul, and swords in the midlands were made to be shorter than other Celtic swords, to preserve iron. Everyone in a tribe was considered family, even slaves, who eventually worked their way into the upper tribal community. Their economic model was a type of anarcho-capitalistic lifestyle, with religion encouraging charity, but never enforcing it. Taxes were taken mostly to provide their leader with a home, improve settlement defenses, and pay their warriors and champions. Soldiers were paid based upon experience, and it was not uncommon for a particular warrior to recieve a large gift for performing a heroic action, such as a pile of silver, or a new weapon or a shirt of mail. In war, champions were a rallying point. They would be banded together as an elite group, whom which the other soldiers would unite with, and follow them into battle; this was an important aspect of British-Celtic war. While the Gauls were similar in some respects, the Britons relied heavily upon champions to inspire them in battle.

As in any Celtic kingdom, their leader is elected, not hereditary. The tribes elect a chief, chiefs in an area elect a chieftan, chieftans elect kings over a larger area, and the kings elect the high king. That is, in a stable kingdom. The Gauls and Goidils successfully managed larger kingdoms in this format for many years, but the Belgae and Britons struggled to attain a remote semblance of order over anything but the smallest of areas. Part of it would have to be enforced through pure military might, to ensure every tribe and region plays along, even when their king is not elected as the high king. In terms of law, the kings had little power; law lay in the hands of judges, elected as well by the people. The higher one's station in society, the harsher the fines and punishment under the law levied against them. Law was central to Celtic religion, and elected officials were meant to be exemplars of the law. A king was a military and business leader, and expected to be intelligent, versed in several languages, and capable of fighting in combat, and intent on leading his men personally when the chance was logically available. The Casse had a king, who ruled over the Casse and their surrounding subservient tribes, such as the Belgic Atrebates, directly. His position was mainly as the organizer of the military, and had a great deal of control in this respect. He also had control of diplomacy, and was the final word in making or breaking alliances. His electors were a kind of 'senate', composed of all the chiefs and chieftans under his rule; after his election, they would also act as advisors. Chieftans and lesser kings acted as generals and lieutenants, and chiefs were captains of local militias. As such, all of them, from the lowest chieftan, to the high king, were elected based on a multitude of issues, but the foremost was their ability to command and lead soldiers. The elected judges formed a seperate 'senate', through which they passed and modified law. This was a slow process; this model was still in use in post-Christian Celtic countries, such as the Irish and Welsh kingdoms, and it's notable that almost no laws changed over hundreds of years. A change to a law would be proposed, and the judge would take this proposal to his tribe. The tribe would vote for or against it, by majority rule, and the judge would return to the conclave, and give the tribe's results. A majority of votes on part of the judges' tribes was required to pass or veto the proposal.

The religion of the Casse, and other Britons, involved dozens of minor local gods, demigods, hero worship, and major deities that would be worshipped over huge regions. Most of their deities tend to be war, health, or legal gods, and their heroes tend to vary between warriors or great poets and storytellers. Among their most important deities are Camulos, a Belgic god of destruction, and Andraste, a British goddess of war. Both require sacrifices, and encourage a large amount of xenophobia toward outsiders; though Britons were remarked as cordial and even warm to outsiders; as well as absolute obedience to the law. Their religion also includes certain ritual aspects, such as painting the body, believing it provided some amount of special, magic protections. They also collect the heads of dead enemies, not just as trophies or signs of bravery, but because the belief that the soul resided in the head. To control a man's head, they believed, meant that his soul had to be your slave, in both this life and the next. The 'druidae', druids, actually didn't come to Britain until around 70 BC, though they'd been in Gaul much longer. However, an essentially identical class, which we casually call druids, was present before hand, and their influence was quite strong. If a higher official was arrested, such as the king, this conclave would also try him, collectively, rather than having a single judge oversee him, since he represents all of the tribes. Likewise, a chieftan would be tried by those judges of the tribes he represents, if he was accused of breaking the law. These systems meant to give each tribe a voice in the events of their kingdom, and the matters of running it.

The Britons were conquered, allied, or otherwise subverted to the Roman powers. During the Roman conquests, Britons fought both as defenders, and alongside the invaders. The Romans withdrew due to constant pressure from both Picti from Caledonia and Goidils (called Scotti) from Ireland. The destruction of silver mines, tin complexes, and encroaching Goidilic slaver colonies and piracy operations made Britain far too unprofitable, especially considering the problems in the other parts of the empire. The Britons continued to exist for a very long time in varied sub-cultures, such as the Cymriae and Cerniuae (Welsh and Corns), the Strathclyders, the Regyddites (who were also partially Gaelic), and the Cumbrians (also had a large Gaelic population). Even today, the Welsh remain a distinct people and are culturally descended from the Britons, though diluted heavily by the Anglo-Saxon and Norman influences from England, and Gaelic influence from Irish colonies established during the dark ages. The Britons never experienced the total Romanization that Gaul did, and their culture was quite resilient and long-standing because of it.