Alright, so this thing? It’s one of the coolest things (I think) the Romans ever did. I was looking up Latin palindromes when I found this. It’s called a Sator Square, and can be read top-to-bottom, bottom-to-top, left-to-right, and right-to-left.
People are still debating the correct translation of the Sator Square’s phrase (“SATOR AREPO TENET OPERA ROTAS”), but the generally accepted translation is “The farmer Arepo has [as] works wheels [a plough].”
But that’s not the coolest bit. Rearrange the letters a bit, and…
…you get a cross that proclaims “Pater Noster,” “Our Father”! The additional A’s and O’s represent Alpha and Omega, which is another reference to the Christian God. So much like the Ichthys symbol, Sator Squares may have been a safe symbol for Roman Christians to protect themselves from Roman persecution.