Religion
Of Celtic religion we know a few superficial facts, but the details that could give us a really deep understanding of their way of thinking has been lost because of the lack of written records. An important feature is the idea of a parallel world and the transmigration of souls. It is said that they thought those who died in this world passed on to the next and those who died in that passed on to this. Some classical writers claimed that Pythagoras learnt his ideas of immortality from the Celts. From the somewhat confused sources, it seems that earlier, the otherworld is not thought to be particularly different from this one, but later, the otherworld is more thought of as an ideal world. Perhaps the worsening of the conditions of life in the diminishing Celtic world has something to do with this, and perhaps also the influence from christianity. But the otherworld is not only the home of those who had died in this world, it seems from other sources that it was the abode of the gods as well, and that some things that were impossible in this world could be done in the other. Maybe we could assume that some things that could be done in this world was impossible in the other as well? Your dreams is an indication, the otherworld is very probably in fact the place of dreams. Human beings and possibly every living thing exist there when dreaming at night. Sometimes you can dream over to the other side when you are awake in daytime, and according to myth, you can cross the threshold in certain physical places where an opening exists. Gifted people, like Bards and other artists, can evoke pictures from the other world, and Druids are taught to act as links from one world to the other.
The Celts evidently believed that material objects also could pass on. Those who died were given all the things that they valued the most to bring with them to the otherworld, which was sometime thought to be underground. On top of the grave, a pile of earth or a cairn of stones was built, often with a ring of poles around it and a pole, a standing stone or an image on top. It was thought that the dead person kept on living there. To the survivors above, the grave functioned as a memorial, and they also thought that the one who resided there took an interest in their life on the topside and protected them. When the Christians started taking the corpses to the churchyard, cairns were built anyway, often at the site of death, and even today, it is a custom to throw stones on them for good luck.
The head has a particular religious significance. Heads of prominent enemies are taken as trophies in war. Heads of especially powerful or wise ancestors are thought to possess strong powers of protection. All Celts wore an open ring around their necks to mark the division between the head and the body. The faculty to store knowledge and skills in the head was greatly valued, and this also is one of the main reasons for their reluctance to adopt writing. In a way, writing is a crutch for memory, and crutches are used preferentially by cripples. What does it mean really to know something? Whether it is a fact or a skill, it requires feeling sure about something that you don't really have material evidence of. If you need to look it up, you don't feel that sure, it's not your knowledge, it's something outside yourself. Neither is the written word any more good than the writer. Much untruth has been written down and cursed whole civilisations for centuries. Without books you have only the real and changeable world to relate to, and if anyone tries to teach you, you can discuss with them. Consider also what books do to the art of storytelling. Lending somebody a book is quite something else than telling them a story you have heard...
Lanon and nemeton are names of shrines, and place names that contain these elements (usually latinised to lanum and nemetum) must have been sacred sites. The Celts generally did not build stone temples like their neighbours in the south, but there are a few remarkable examples from the southeastern "Province" of Litavia, evidently a result of early Graeco-Roman influence. But many places have remains of large buildings often of a square layout instead of round like the most common Celtic dwellings, and these seem to be some kind of sanctuaries. They are usually placed somewhat apart from the other buildings, and may contain an inner square chamber inside the outer walls. Possibly, the Greek temples are a model for these structures as well. The Romans built round stone temples in Gaul and Britain, and in several cases, timber structures of the same shape seem to have been there before them. Other places, only groups of posts are found under them, surrounded by round ditches.
Few such temples are known from historical literature, where the usual story is that the Celts worshipped their gods in clearings in the depth of the forest. The only temple I know of being mentioned with a specific location in the literature lay on an island, apparently otherwise uninhabited. The original meaning of the word nemeton is usually said to be a sacred clearance in the woods. Several sites are found with a more or less isolated location and a probable religious significance. They are usually surrounded by round or elongated rectangular ditches which may have been supplemented by palisades. Often, they contain a few graves, probably of people whose spirits the builders depended on for protection, and a number of postholes in a regular pattern. In such a posthole, a skull of an ox was found, and this could indicate that the post may once have been adorned with the head of an ox. Large quantities of animal bones indicate sacrifices. Human bones are found some places too. At some of these sites, pre-Celtic graves and other remains are found.
Another interesting feature is the sacrificial or funerary wells. They are dry pits usually found within the area of one of the types of sanctuaries mentioned above, and they are found in the whole of transalpine Gaul, the Belgian area of later Germania and also the Belgian area of Britain in the southeast. But some of them are very old, the oldest objects being dated to around 1500 BCE, an age usually regarded as pre-Celtic. They are often 10-12 meters deep, and some of them have an intricate masonry superstructure with a small opening on top. In the bottom, often a large, upright stake is set down, exceptionally a whole tree. One has a full-size seated woman figure at the bottom. They are filled with various objects, sometimes valuable, but also bones of men and animals, wooden figures and pots, usually whole, they are lowered down carefully and not thrown down. Ritual pits are known from classical civilisation as well, Latin mundus, Greek bothros. They were used to communicate with divinities from the subterranean otherworld. Favissa are shafts in sacred places where objects that have been sanctified from being used in the ritual are buried along with bones or ashes from the sacrifice. It is proposed that the Celtic religion also may have had these functions.
There are many sacred wells, springs and pools, some of which have been in use to the present day. Originally a head or skull is the guardian of the spring, which it is a mortal sin to remove. Many places, there is a drinking cup fashioned from a skull. These waters often are brimful with votive gifts that have been deposited for centuries, often valuable, tons of gold, silver and bronze are found. If the water is thought to be healing, it will often be full of figures, usually wooden, with the sick member emphasised. Maybe the sick persons themselves cut these figures to bring with them on the pilgrimage to the holy water. Another favourite for gifts to the gods are great cauldrons, a symbol for plenty and regeneration. The cooking pot was central in the home, and Celtic mythology contains numerous stories of holy and magic cauldrons, the holy grail being one of them.
The Celtic religion is one of those where the number of deities is just about endless. It can be classified as animistic, everything in nature seems to have a divine nature and spirit. Many of the deities are purely local, connected with wells, mountains, groves, or with the clan. But some gods and goddesses are more global and worshipped by all Celts. Dis, also known as Uxellimos (the highest) or Taranis, Taranucos (the thunderer), is the ruler of the otherworld and the ancestral father of all Celts. Teutates is the protector of the whole Celtic nation, the highest of all tribal gods and the friend of the humans in their fight for existence. Tribal gods of certain individual states also are worshipped outside their boundaries, like Olloudios of the Narbonnense, Lenos or Ocelos of the Treverii, Vellaunos of the Allobroges, Esos of the Essuvii, Camulos of the Remi and Brigantia of the Briganti. But Lenos, Ocelos and Vellaunos seem to be identical to Belenos (the sparkling, shining), who is celebrated on May Day and said to be a sun god, god of light and fire, father of gods and men and the consort of the mother goddess. Another extremely popular god of light and fire is Lugos. Deai Matres is a general plural name for the mother goddess, who is worshipped in many forms and under many names in different places and guards many sacred places. The most common names are Ana, Anna and Dana. In the continental Belgian areas, she is known as Virodactis.
Epona is the enormously widespread and popular horse goddess. She is often depicted on horseback with a fruit basket which also symbolises fertility. More than 300 Epona altars are known from France. Cernunnos is a hart- or deer god endowed with horns and animal ears, not a really widespread god in ancient times, but he has become popular in modern times. Ambactanos is an agricultural god. Annona a goddess of the harvest. Rosmerta is a fertility goddess, depicted with a staff, a serpent and a money pouch. Erriapos seems to be a god of the forest and vegetation. Ialonos Contrebis is a Britannic god of the clearance in the woods. Granna is the Sun goddess, or Grannos the Sun god. Leucetios is the god of lightning, Vintios of the wind, and Vitucadros in some way is connected with shining energy. Setlocenia is the goddess of long life. Agrona a Britannic goddess of death and slaughter. A god of war in general is Albiorix (king of the world). Caturix (battle king) and Belatucadros are worshipped by lower ranked military and Cocidios is said to be the god of soldiers. Some states had their own gods of battle, like the Remian Camulos and the war goddess Adraste of the Iceni.
Sequana, Sirona and Sulis are goddesses of sacred springs who are worshipped several places. Rivers are worshipped as gods, e.g. Danuvios (Danube), Tamesis (Thames), Axona (Aisne), Matrona (Marne), Ritona (Rieu), Adsalluta (Save), Clota (Clyde) and Belisama (Ribble). Sequana is a river as well (Seine). Some of these river gods have extended their influence, and many of them are worshipped still in some way. Other, nameless spirits are known under general names like the dervonnai, oak-spirits, niskai, water-spirits, and, og proximai, seemingly connected with female relatives.