By many ancient traditions, the solstices are the Middle of their respective seasons (as in Shakespeare’s play “A Midsummer Night’s Dream”). This is especially true in an agricultural society. It is our modern society that has renamed the solstices as the start of the seasons instead. In the Celtic tradition, the seasons were marked with special celebrations:
* Samhain marks the beginning of winter and is celebrated at the end of October or beginning of November.
* Imbolc marks the beginning of spring and is celebrated at the beginning of February.
* Beltane marks the beginning of summer and is celebrated at the beginning of May. In much of the northern hemisphere, this is when crops can safely be planted as the danger of frost has largely passed.
* Lughnasadh marks the beginning of autumn and is celebrated at the beginning of August. In much of the northern hemisphere, this is when the harvest begins, with most of it complete within 45 days (mid-September) to avoid the first frosts.
These four dates are also known as cross-quarter dates and are approximately mid-way between the solstices and equinoxes. The solstices and equinoxes were also celebrated with festivals, but I don’t think they were as important as the seasonal celebrations.