Germanic boar helmets are attested in archaeological finds from England and Sweden, dating to Vendel and Anglo-Saxon periods, and Old English and Old Norse written sources. They consist of helmets decorated with either a boar crest or other boar imagery that was believed to offer protection in battle to the wearer. They have also been proposed to be a costume for the ritual transformation into a boar, similar to berserkers, and to be associated with Freyr. The boar was an important symbol in prehistoric Europe, where, according to the archaeologist Jennifer Foster, it was "venerated, eulogised, hunted and eaten ... for millennia, until its virtual extinction in recent historical time." Anglo-Saxon and Vendel era boar symbols are preceded by a thousand years of similar iconography, coming after La Tène examples in the fourth century BC, Gaulish specimens three centuries later, and Roman boars in the fourth century AD. The boar is said to have been sacred to a mother goddess figure among linguistically Celtic communities in Iron Age Europe, while the Roman historian Tacitus, writing around the first century AD, suggested that the Baltic Aesti wore boar symbols in battle to invoke her protection. Four legions, including the twentieth that was stationed in Britain, also adopted the boar as their emblem. The sole unequivocal depictions of boar-crested helmets outside of Germanic sources are on interior plate E of the Gundestrup cauldron, dating to the La Tène period or early Roman Iron Age, which is commonly believed to be Celtic in origin but also has elements suggesting Thracian origin. Boars had a prominent role for the Germanic peoples and were closely associated with battle. The boar's snout formation was a wedge formation first attested in the 4th century AD, used by the Germanic peoples and named due to its appearance. The formation was also used in the medieval period, as attested in sources such as Knýtlinga saga and Ólafs saga Tryggvasonar.