The First Empire of Britannia, also known as the Britannian Empire, the Reformed Western Roman Empire and the Londinium Empire (479-1098) was an important and powerful "Intercisus (Broken/Severed) Roman State," one of many such nations formed throughout history to claim the mantle. While not the first (the Eastern Roman Empire was the first), the First Empire of Britannia was perhaps one of the most successful. Founded by Britannian-Roman Julius Vavro in 479 after uniting the towns of south-eastern Britannia to face the Saxon invaders from across the North Sea, and then capturing the city of Londinium and declaring it his capital, reforming the Senate and bringing more regions of Britannia into the Empire.
Under the Reigns of Emperors like Claudius II (697-728), Julius V (750-782) and Anthony IV (824-853), the Britannian Empire expanded to encompass Caledonia and Hiberina, lands that even the ancient Roman Empire had been unable to claim in what was to be called the Lux Britannia. Dreams of further glory and empire building on the continent also lead to an empire stretching from the land from Britany in the east to Jutland in the west, controlling the Channel of Britannia and the North Sea with it's powerful navy and disciplined armies. However, over-expansion, attacks by the Norse/Vikings on it's holdings, plague from 850-864, and the early death of Anthony V (853-857), and the lack of a heir to replace him lead to a long series of brutal civil wars between generals, senators and claimants to the throne lead to the loss of it's European holdings by growing European powers, and eventually the fracture of the Empire in the Britannian Isles. The death of the last Emperor Harold II (1094-1098) while defending his capital of Dublin in Hibernia marked the end of the era, and the start of the Britannia States period (1098-1351) when no single power could claim control over all of Britannia.