Celts used the cross-quarter days to mark the change of the seasons and their midpoints rather than the Solstices & the Equinoxes.
The ancient Celts divided the year into two main seasons.
Winter (Samhain) and Summer (Beltane) with Imbolc and Lughnassadh representing the midpoints of these seasons.
At Beltane, the ancients would perform rituals to protect the cattle, crops, and people as well as to encourage growth and fertility.
It is believed that during these two points of the year, Samhain and Beltane, the veil between our world and the Otherworld thins.
This allows the spirits of the dead, fairies and other supernatural beings roam freely.
To prevent people from ending up in the Otherworld, crop failures, and livestock mischief, protection rituals were traditionally practiced against the enchantments of supernatural beings to protect those of this world.
On the Beltane cross-quarter day the ancients Celts would build two bonfires and herd all their cattle and other stock between them as a cleansing and purification ritual to protect them against supernatural forces before being set loose on their new spring pastures.