I have also seen where priests will use a beautifully embroidered cloth with the relic of a saint sewn into it and celebrate Mass over that. I don’t know what the name for this is, but I assume most Traditional priests and all pre-Vatican II priests used one of these things whenever they celebrated Mass if they couldn’t celebrate Mass on a real altar. I have seen my priest use this before when he had to say the Mass in a Novus Ordo church that no longer had a high altar. The Orthodox use this item even on their altars in their churches, instead of having altar stones.