Railroad ties make a good retaining wall. Heavy and thick, they’re impregnated with creosote so they’re nearly rot-proof. Peg them together with 3/8″ rebar and they’ll be there 20 years later (according to this picture. Neighborhood has sure run down since I lived there.)
The process is to lay down the first layer of ties, drill holes where the pins will go through, lay down the next layer, drill, and repeat. Somehow, I kept performing the miracle of drilling the holes exactly where they needed to be. Stupid confidence sometimes turns into wild good luck.
I’d finished the fronts of the walls, tied into the sides next to the steps. I do not remember why (trauma, perhaps) but as I neared the end, I asked my teenage son Tristan to come help.
“Here, hold this,” I said, with a 3-foot chunk of rebar placed in the top of the hole in the railroad tie.