Four concrete blocks, all 8 x 8 x 16, but one of them configured slightly differently, as shown.
You get the essential info in the first 30 seconds of the video. Voila!
I’m going to purchase our four blocks today, when Rebecca and I go get all the stuff to create our pine bough wreaths this evening for our Holiday Open House next Wednesday evening. BTW: check out the new revised facebook page for Green Acres Neighborhood Garden. My podmate Katarina is doing a bang-up job, putting up lots of permacultural posts as well. She and I would be grateful if you go there and add your “like” to the page! Thanks.