The Celtic festival of Imbolc marks the midpoint between the winter solstice and the spring equinox. It was associated with the Goddess Brigid, and in Christian times it became Candlemass or St Bridget's Day, celebrated today on 1st February.
Imbolc, as Welsh speakers will know, means 'in the belly' and it is commonly thought to link to ewes giving birth. This is probably unlikely: although sheep today generally lamb in February, in Iron Age times they would lamb later - March or April - to take advantage of the spring grass and better weather.
Imbolc is more likely to link to human pregnancy, falling nine months after the fertility festival of Beltaine on 1st May. A lot of babies conceived at Beltaine would be born around this date.
This links to an interesting point. Before modern medical advances, life and death were more intimately connected to the seasons. Infant mortality rates were high and varied greatly throughout the year. The most ideal time for a birth in Celtic Britain - giving the best chance of survival for the newborn - was around 1st February. The worst of the winter hardship and shortage of food was past, spring plants were beginning to shoot, providing valuable nutrients for nursing mothers, and the baby had a good period to develop a strong immune system before the summer heat led to a surge in disease.
Was the Beltaine fertility festival developed specifically for that reason? Answers on a postcard please.