Diodorus Siculus remarked that the Celts believed strongly in the immortality of the human soul. One piece of evidence he offered in support of this view was the fact that mourners threw letters to the dead onto the funeral pyre. But this may not have meant that the dead were believed to live for all eternity—it may only imply that there was a short time after death when the spirit of the dead person was still close by and might be communicated with. In fact, many of us have had the experience of visiting the house of someone who has recently died, perhaps to clear their belongings away in readiness to put their house up for sale, and had the powerful impression of the dead person’s continuing presence. It is easily explained by the arrangement of all the dead person’s possessions, arranged in a characteristic way, conveying the personality, and implying that the dead person has just left the room and may return at any moment. In an archaic society such as that of the ancient Celts, that feeling would have been just as strong. But it is because of this type of feeling that, in common with all societies, archaic or advanced, we have funerals. There has to be a leave-taking, a moment of separation when we let the dead person go and when we return to our own lives again. In our advanced and largely secular society, a society in which few people believe in the survival of the human soul, we still write messages to the dead and leave them flowers.
There is nevertheless other evidence that the ancient Celts believed in the immortality of the human soul. Writing about the Druids, Julius Caesar said, “A lesson they take particular pains to inculcate is that the soul does not perish, but after death passes from one body to another.” In other words the Celts believed in reincarnation.
In Gallic Wars, Julius Caesar comments about Celtic religious beliefs:
The Druids attach particular importance to the belief that the soul does not perish but passes after death from one body to another; they think that this belief is the most effective way to encourage bravery because it removes fear of death.
This belief carried over into the idea of shapeshifting, where some beings could adopt a new life-form without even the separating pause of death.
A number of classical writers tell of a warrior elite existing in Gaul and Britain, second in rank to the warrior king. This elite was associated with rich and elaborate graves, and the richness of the grave goods strongly implies that there was a belief in an afterlife in which all the gear necessary for good living would be needed. There was also an elaborate funeral in which these grave goods were assembled. Again, Caesar commented on the practice in Gaul:
Although Gaul is not a rich country, funerals there are splendid and costly. Everything the dead man is thought to have been fond of is put on the pyre, including even animals. Not long ago slaves and dependants known to have been their master’s favourites were buried with them at the end of the funeral.
All this points to a belief in an afterlife. Lucan expressed it as a belief in a long life in which death was merely a pause, a bridge between one life and another.
This belief seems to have been real. There were many burials where pairs of hobnailed boots were provided, perhaps to wear for the journey to the Otherworld, or to wear once there. At Cambridge, infants were buried with shoes that were far too big for them; apparently their parents nursed the hope that their children would grow into them as they grew up in the Otherworld.
The Irish had a strong tradition of reincarnation, perhaps several times. The King of the Land of Promise, Manannan, had magical powers, including the power to give new life. Manannan is of interest because he is associated with a real historical figure, the Irish King Mongan, who lived in the seventh century AD.