The Roman writer Tacitus provides us with the only Roman account of the Druids in Britain:
Tacitus Annals XIV
He [Suetonius Paulinus] prepared accordingly to attack the island of Mona, which had a considerable population of its own, while serving as a haven for refugees; and, in view of the shallow and variable channel, constructed a flotilla of boats with flat bottoms. By this method the infantry crossed; the cavalry, who followed, did so by fording or, in deeper water, by swimming at the side of their horses.
On the beach stood the adverse array, a serried mass of arms and men, with women flitting between the ranks. In the style of Furies, in robes of deathly black and with dishevelled hair, they brandished their torches; while a circle of Druids, lifting their hands to heaven and showering imprecations, struck the troops with such an awe at the extraordinary spectacle that, as though their limbs were paralysed, they exposed their bodies to wounds without an attempt at movement. Then, reassured by their general, and inciting each other never to flinch before a band of females and fanatics, they charged behind the standards, cut down all who met them, and enveloped the enemy in his own flames.
The next step was to install a garrison among the conquered population, and to demolish the groves consecrated to their savage cults: for they considered it a pious duty to slake the altars with captive blood and to consult their deities by means of human entrails. While he was thus occupied, the sudden revolt of the province was announced to Suetonius.
Three figures dressed in cucullus (found on a shrine on Hadrians wall). The Druids may have worn similiar attire
Notes to help interpret Tacitus' account
In this scene Tacitus describes the Druids as "lifting their hands to heaven" which is in keeping with some Celtic images that we have of their shamens in prayer. They are described as cursing and under the circumstances it seems reasonable to assume that they would have been requesting the Gods to avenge the Roman invaders. We have Celtic descriptions of 'Druids' cursing (one hand, one eye, one foot) in a similar way to the Buddist monks of Tibet. That they formed a circle would imply that they believed that some sort of power was derived from this ritual. Tacitus may have had access to Roman military accounts but whether or not the words he records are those of the Roman commander or his own literary invention he implies that the Druids were fanatics.
In his description of the subjugation of the island, Tacitus provides further justification for the attack on this religious order. He paints the Druids in the worst terms for his Roman audience and without mention of the intellectual prowess accorded to them by many other classical writers. He is writing as a Roman and there is reason to suspect that his account is tinged with the propaganda of the conqueror. Tacitus' description of the sacred groves and altars slaked in blood is similar to that given by the Roman writer Lucan writing about Julius Caesar's encounter with a site near Marseilles in Southern Gaul: "Interlacing boughs enclosed a space of darkness and cold shade, and banished the sunlight from above. ... Gods were worshipped there with savage rites, the altars were heaped with hideous offerings, and every tree was sprinkled with human gore. On these boughs ... birds feared to perch; in those coverts wild beasts would not lie down. ... Legend also told that often the subterranean hollows quaked and bellowed, that yew-trees fell down and rose up again, that the glare of conflagration came from trees that were not on fire, and that serpents twined and glided round the stems. The people never resorted thither to worship at close quarters, but left the place to the gods. When the sun is in mid-heaven or dark night fills the sky, the priest himself dreads their approach and fears to surprise the lord of the grove ( dominum luci )." 
The Celtic place names 'Nemeton' and 'Llanerch' are associated with Celtic religious centres. These words can be translated as a clearing in the woods and this seems to support the idea that the clearings in the woods rather than the groves themselves were the central place of worship. Old trees like the yew and the oak were important to their religion and the title Druid or Derwyddon in Welsh actually means oak knowledge. The yew tree (as mentioned in Lucan's poem above) also seems to have been associated with these places and it survived in the Welsh 'Llan' or churchyards of Celtic Christianity. Some yew trees like the bleeding yew at Nevern in Pembrokeshire actually wooze out a red sap which looks like blood. These early Christian enclosures followed the same circular plan of the pagan religious centres that they supplanted.
Whist Tacitus' account may be tainted with predjudice it also seems to contain more than a grain of truth. Some modern schools of thought tend to argue that the Roman sources are wrong about the Druids performing human sacrifice but this is to ignore the historical and archaeological records. The evidence of human bodies ritually strangled and placed in bogs etc. The Gundestrup Cauldron shows that cauldrons were used to ritually drown their victims.
The Gundestrup Cauldron shows Celtic warriors being ritually dunked into the cauldron of rebirth
In a similar fashion the captives of the Cimbri are recorded by Strabo as having their throats cut over a cauldron: "Their wives, who would accompany them on their expeditions, were attended by priestesses who were seers; these were grey-haired, clad in white, with flaxen cloaks fastened on with clasps, girt with girdles of bronze, and bare-footed; now sword in hand these priestesses would meet with the prisoners of war throughout the camp, and having first crowned them with wreaths would lead them to a brazen vessel of about twenty amphorae; and they had a raised platform which the priestess would mount, and then, bending over the kettle, would cut the throat of each prisoner after he had been lifted up; and from the blood that poured forth into the vessel some of the priestesses would draw a prophecy, while still others would split open the body and from an inspection of the entrails would utter a prophecy of victory for their own people; and during the battles they would beat on the hides that were stretched over the wicker-bodies of the wagons and in this way produce an unearthly noise." (3)
It is unlikely that the Druids themselves would have regarded these sacrificial acts as 'pious' as Tacitus indicates but more likely as necessary to recruit the help of their Gods. Offerings were made to the Gods in return for protection and good fortune and this is common to many religions. The ritual deposition of items in Llyn Cerig Bach in Anglesey include swords, spears, chariot fittings, horse bridles, cauldrons, a trumpet, currency bars, animal bones and two sets of slave chains. Many of these items were damaged before they were put into the lake and symbolise the destruction of wealth which is being given to the Gods. From the archaeological record it generally seems that human sacrifice was not as common as the provision of other gifts to the Gods. However, in the case of Llyn Cerig Bach the resident engineer on the excavation recorded human remains too but these did not appear in the report written by Cyril Fox who did not conduct the excavation and may have had reason to hide such a find. (2) Other similar sites have invariably included human remains. The bodies found at Lindow Moss and in particular Lindow man do show us that human sacrifice was definatlely taking place at the time of the Roman invasion of Britain. For the Celts, the ultimate sacrifice was a human one which might have been considered necessary in certain circumstances, for instance if the Romans were coming to take your land, destroy your power and culture and kill anyone who resisted! The extreme religious practices of the Celts don't sit easy with the modern mind and so most of the Pagan reconstructionists of today deny that it was part of the religion of these ancient people. The Roman writers may also have been equally horrified by what they call acts of savagery but it was used as an excuse for the destruction of the power of the Celtic people. Whilst the Romans attempt to take the moral high ground we should remember also the savagery of the Romans who themselves performed the ritual sacrifice of the Gallic leader Vergingetorix in the Colosseum not to mention the execution and horrific deaths of countless Christians and others in the name of entertainment.
There is probably artistic licence in Tacitus' description of the women who were amongst their adverseries on the shores of Anglsey but at the same time it is quite likely that there were women amongst the British who were encouraging their men who were about to do battle. The women in the description are likened to the 'Furies' of classical mythology who were the furious avengers of wrongful deeds. These mythical women are indeed depicted as being robed in black and are often depicted brandishing torches or sometimes snakes. To Tacitus' Roman readership the description would have emphasised the strangeness of the Celts and would also have been symbolic of Celtic irrationality versus the good sense of the Romans. Playing along with Tacitus and in the context of the Druids the description of the women dressed in black reminded me of 'gwrach' or witches. The Furies also symbolised vengeance and rebirth and Tacitus' analogy may have been a good one given the revenge that Boudica and the Iceni were about to inflict on the Romans.
Orestes tormented by the Furies for killing his mother
The causes of the revolt of the Iceni led by Boudica tend to be viewed in isolation from the events that occured in Anglesey even though the Roman forces were recalled from there to deal with the revolt. The Romans attack on the religious heart of Celtic Britain would surely have been viewed very gravely by all of the Celtic tribes. The Iceni's attack on the Roman Capital of Colchester may not have been the best military target but it was their religious centre in Britain and had previously been an important religious centre for the Iceni.
Some have argued that Suetonius' recall from Anglesey to deal with the revolt of the Iceni allowed elements of Druidism to survive. Others argue that it died there and then. Although we are told that Anglesey was the Druidic centre it does not follow that all Druids were in Anglesey at the time of the attack. The Roman writers tell us that during the Boudica Revolt which followed that the Iceni performed sacrifices to the Goddess of revenge, Andraste. They also tell us that the Celts will not perform sacrifices without their Druids. By inference there appear to have been Druids amongst the Iceni. However, the attack on Anglesey was undoubtably a crippling blow to Druidism and whilst elements of it did survive in remote parts of Britain and in Ireland they would never weild such power again. More importantly perhaps the collective memory of the illiterate British tribes was also dealt an almost fatal blow for the Druids were the retainers of that knowledge.
It is interesting to note that the Romans only ever banned two religions and they were the Druidic practices and Christianity. They were banned because they were considered to have a powerful influence. The Druids were probably more of a threat than the Celtic chiefs as it seems that they were trying to co-ordinate attacks on the Romans. The Romans policy was to divide and rule and it was a shrewd move to try to eliminate them even though it probably added fuel to Celtic anger and was almost certainly a contributing cause in the Boudicca revolt.
 Nora Chadwick, The Celts, Penguin books, 1991 p. 146
 Strabo gives this vivid description of the Cimbric folklore ( Geogr. 7.2.3, trans. H.L. Jones)
Article © Nigel Cross 2009