an important and unifying aspect of Celtic cultures such as the Hallstatt culture, La Tène culture, Gallic and Brittonic cultures; no remains of these vehicles from the period have yet been discovered in Ireland. Tribal warfare Endemic warfare appears to have been a regular feature of Celtic societies. While epic literature depicts this as more of a sport focused on raids and hunting rather than an organized territorial conquest, the historical record is more of different groups using warfare to exert political control and harass rivals, for economic advantage, and in some instances to conquer territory. Celtic peoples fought amongst each other; sometimes they allied themselves with the Romans, Greeks, Carthaginians, Etruscans, Macedonians, Germanic peoples and various other peoples against each other and against other Celtic groups. The organizational structure of Celtic tribes and societies varied greatly with some groups having strict hierarchical structures and a ruling monarchy, while others exhibited representational organizational structures typical of a Republic, especially by the time of the Gallic Wars. Historical Celtic groups included the Aquitani, Belgae, Bituriges, Boii, Britons, Caledonians, Celtiberians, Gaels, Galatians, Gallaeci, Gauls, Helvetii, Lepontii, Noricum, the Picts and the Volcae. These groups often produced cultural offshoots through descent, diffusion, migration and Celticisation. Archaeology provides much information regarding the material culture of the Celts, especially that of the La Tène culture and Hallstatt culture. However, the significance of these finds in determining how the ancient Celts actually fought is the subject of much speculation and debate. It was long thought, for instance, that the Celts were headhunters, but recent research from France has indicated that it may have been the heads of slain allies that were collected to be placed in porticos, while the defeated were dumped in mass graves, their weapons ritually broken. Hallstatt Cultures 1200 BC to 450 BC The Hallstatt Culture is the earliest to be identified as associated with Celtic culture, spreading from north of the Alps west into France, Southern Britain and the Iberian Peninsula. The earlier phases of the Hallstatt era fall into the Bronze Age. Swords seem to have been the primary weapon from this period, perhaps indicating that warfare was a relatively small scale affair, possibly between groups of elite warriors. In the latter phases of the Hallstatt era, iron began to replace bronze in the manufacture of weapons, and the classic "Celtic sword" with its leaf-bladed design made its appearance. Chariot burials