This is the time of year that people invariably ask me about Thanksgiving in the Middle Ages. Did they have it? What was it like?
Tolkien tells us, "Go not to the elves for counsel, for they will say both yes and no," and the same could be said about academics. The answer about medieval Thanksgiving is both yes and no.
Let's start with the "no." Thanksgiving as Americans think about it is a national holiday. Though the general idea of thanking God for the harvest is so ancient as to be pre-historic, for Americans it is also tied into a particular historical moment: The first (American) Thanksgiving at Plymouth* in 1621, when the pilgrims invited the Wampanoag indians to join them in thanking God for saving them (with the Wampanoag people and their interpreter, Squanto, as God's presumed primary instruments).
So in that sense, Thanksgiving is a strictly American holiday. That being said, it is part of a broad, global ritual of thanking God (or the gods) for the harvest, and so is not at all particularly American.
Lots of other countries have harvest festivals today, called any number of things, including Thanksgiving. Indeed, I've never lived in any country that didn't have some kind of harvest festival, but it may be that some cultures don't. Whether you're thanking Demeter, or the spirits of your ancestors, or the Christian God, the general forms are similar -- a merry feast of thanksgiving.
So what about the Middle Ages? Well, if you think about the liturgical calendar, you'll see that there are lots of feast days just as there are days for fasting. Those feast days often functioned much as we might consider Thanksgiving. Indeed, a town with a local saint whose feast day was in the fall might find very little gap between the saint's day and the harvest celebration.
Want an example? Read the opening of Sir Gawain and the Green Knight -- the setting is a Yule celebration at Camelot. Yule, of course, is today closely related to Christmas, but if you read the description it will also sound a lot like Thanksgiving. In that description I think we see an idealized version of what a medieval harvest festival might look like.
What did they eat? This is a tough one, since the "Middle Ages" spans many centuries and spills over from Europe onto north Africa and west Asia -- it no doubt differed from place to place. One place might have pork as a tradition, while another might have goose, while another might have venison. Some of the foods Americans traditionally associate with Thanksgiving are New World resources, and so would definitely not have been eaten, turkey being the prime example of this.
Regardless of what you eat or what you call it, Thanksgiving is part of a tradition that stretches back beyond the Middle Ages, probably into pre-history. Agrarian societies are very aware of the various forces beyond are control that can lead to a good or lean harvest, and even today when most of us don't grow our own food, we see that forces beyond our control can shape our financial ability to buy that same food. Even today, we understand that we need to thank God for all we have.
*Yes, I know you Jamestown folks claim the first, so please don't write any angry e-mails. I'm talking about the popular imagination here, and outside of Virginia, when people think of the first Thanksgiving they think of Plymouth.