It's called a doufeu, which means 'slow heat' in French
You put ice cubes in the depression of the lid which cause steam released by cooking liquids to collect on these tiny bumps on the underside of the lid. The steam condenses into droplets of water which then sprinkle the meat and/or veggies cooking below keeping them moist and succulent. You can also use the pot without ice in the lid as a regular braise pot.
I asked the price and the vendor told me 40 euros adding...'it's a good price, Madame.' I told him I'd think about it. While the pot appeared to be of good quality, I didn't recognize the brand. Maybe 40 euros was too much?
When I returned home, I googled 'Cousances' and this is what I found. It's a very old French company founded in 1553. It was purchased by Le Creuset in 1957 and basically all they did was stamp the Le Creuset name on the bottom of Cousances pots! So, I do have a Le Creuset pot after all. I read a critique of both pots and learned that the enameling on the vintage Cousances pots is actually considered superior to Le Creuset as are the pot handles. Le Creuset scores higher on color choices, though. Most of the Cousances vintage cookware I can find for sale online is on eBay and only one piece was similar to mine. It was offered for $120 which is about double what I paid for my pot. I guess the seller was correct...40 euros was a good price!
Now I just have to learn how to use my doufeu!