On the Atlantic façade, megaliths are a characteristic of Brittany in general, especially of the Morbihan area, but they can also be found across the Channel, in Ireland and the other Celtic countries east of the Irish Sea, and at the southernmost part of the Atlantic façade, that is Portugal. Research is in progress, but when confronted with unmovable and speechless artefacts, archaeologists may have a hard time finding an interpretation for some characteristic engravings. The history of religions can help interpret some of those artefacts, thanks to a few basic concepts on pre-Christian beliefs about the origin of life, involving deer and the role this animal might have had in our ancestors' mind, back in the Mesolithic but also in the Neolithic eras. Hopefully this animal, unnoticed until now by archaeologists, will find its due place in a world dominated by man, and will also help make things clearer between Irish and Breton megalithism. Their relationship has remained unclear in spite of Michael Herity's 1974 hypothesis1 on the Breton origin of Irish passage tombs. This origin remains unchallenged in Alison Sheridan's 2003 contribution, in which, however, the emergence of passage tombs is much older than previously thought. Provided progress in archaeology makes it possible, this paper will first examine the likely origins of Breton megalithism, between Barnenez and the Morbihan. It will then examine the relationship between hunter-gatherers and agriculturists, their possible melting, their migration to Ireland around 4000 BC and, through a comparison with related cultures, some of them very far, the unexpected importance of deer in their mythologies and their rites. The paper will then focus on the figure of Anna, and suggest that she runs throughout the cultural layers that have succeeded one another in these two regions, Ireland and Brittany. This anthropomorphic Neolithic female figure, who probably replaced the zoomorphic Mesolithic one in Brittany, both of them anonymous, probably originates from Anatolia where the agriculturists came from as soon as the 7th millennium BC. She was probably given her name, Ana, by the Celts of the first or second Iron Age, at the time when their culture was dominant in the region. Of course, in Turkish Ana today means ‘mother’ but it is an Indo-European word. It will also be suggested that Irish Celtic sovereignty, applied to the land considered as a mother, must have been a new concept for these hunter-gatherers and agriculturists. Eventually, the paper speculates that in these two regions, Ana may be viewed today as the syncretic symbol of the female figures of each successive people and civilizations.