At the time of the Roman occupation of Wales (first century CE), the Ilse of Mona (now Anglesey) was one of the last strongholds of the Celts and their druidic priests. The Romans decided that it was vital to invade Mona and destroy the Druids, who were maintaining native resistance against the Romans. The Roman historian Tacitus gives an account of the ensuing battle on the shores of the Menai Straits:
On the opposite shore stood the Britons, close embodied, and prepared for action. Women were seen running through the ranks in wild disorder; their apparel funeral; their hair loose to the wind, in their hands flaming torches, and their whole appearance resembling the frantic rage of the Furies. The Druids were ranged in order, with hands uplifted, invoking the gods, and pouring forth horrible imprecations. The novelty of the fight struck the Romans with awe and terror. They stood in stupid amazement, as if their limbs were benumbed, riveted to one spot, a mark for the enemy. The exhortations of the general diffused new vigour through the ranks, and the men, by mutual reproaches, inflamed each other to deeds of valour. They felt the disgrace of yielding to a troop of women, and a band of fanatic priests; they advanced their standards, and rushed on to the attack with impetuous fury.
The Britons perished in the flames, which they themselves had kindled. The island fell, and a garrison was established to retain it in subjection. The religious groves, dedicated to superstition and barbarous rites, were levelled to the ground. In those recesses, the natives [stained] their altars with the blood of their prisoners, and in the entrails of men explored the will of the gods. While Suetonius was employed in making his arrangements to secure the island, he received intelligence that Britain had revolted, and that the whole province was up in arms.
Stories about Druids
Writings on Celtic Sacrifices