Harvesting the wheat fields. (photo: tpmartins/Flickr, CC BY-NC-SA 2.0)
During medieval times, Christians observed this day as a feast day of St. Peter in Chains. The Anglos-Saxons called it hlaefmass, or “loafmass” in which medieval Christians baked bread from the first wheat grains harvested and placed loaves on the church altar as an offering. The festival, rooted in Celtic origins, marks the beginning of the harvest season and the middle of summer — the midway point between the summer solstice and the autumnal equinox. Lammas is a time of thanksgiving for the ability to reap a successful grain harvest.
Celts held the fire festival Lughnasadh at this time to honor the Irish god Lugh, who is associated with late summer storms. And this is also called the season of John Barleycorn, the personification of the barley crop.