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Since you seem to know this game, what about the castling? The description in the CVP article was totally confusing for me. So I only implemented the Dababba leap that was mentioned, as an initial move.

For those interested in history, the move of the Champion of Arciscacchiere invented by Piacenza is clearly only crossing empty squares when "travelling" two squares as Rook or Bishop (p118). So, the Centurion cannot leap occupied squares as Alfil or Dabbaba. Piacenza insisted on this point several times in his description. (ex p119,p123). In Betza notation it is NnAnD. The Centurion is not a Squirrel.

However, Murray did not understand correctly and described the Centurion as a jumper in the eight directions. Pritchard repeated that definition given by the English historian and added the Knight’s leap that Murray had forgotten. He had forgotten it because Piacenza explains to have added the move of the Knight only few pages later. (The presentation of the rules by Piacenza is a bit messy).

So few pages later (p120), Piacenza confessed to have spoken with a certain Mr. Fantone which would have allowed him to have seen a chess book in which a Centaur also had the Knight’s power. Piacenza decided to adapt this idea in order to allow his new piece to reach any square on the board (otherwise the Centurion would have been color-bound and limited to half the board).

So, Piacenza’s Centurion jumps when moving like a Knight but does not leap on the rows, columns and diagonals.

In my opinion, the CVP would be inspired to give the genuine rules and not the wrong ones.

Piacenza's book is findable on the Internet. I can provide the photographs of those pages if someone is interested.

Last word for HG: there is nothing about a specific en-passant rule in that description of Arciscacchiere by Piacenza. So your implementation is not incorrect in my opinion. The description of this variant being at the end of Piacenza's technical book about chess, it is possible that this peculiar restriction was given for the orthodox chess that was presented by Piacenza. Then, someone would have extrapolated to the large chess variant as well. Again, we are not obliged to follow this as it is not written.

i think so

the rook moves one or more squares towards the original position of the king; the king moves one or more squares towards the original position of the king.

Shouldn't the last word there be "rook"?

ArchChess in the 17th century has what we call now Squirrel, D+A+N. Recently there was Hippogriff found in Tamerlane Chess of 14th century, where Hippogriff restricts 13th century Grande Acedrex Gryphon to its distant squares. Tamerlane or Timur's also has Dabbabah, so the Dabbabah had been around for ArchChess to pick up and make the probably first tri-compound it calls Centurion, settled on as Squirrel or Betzan AND today -- the order does not matter in Funny Notation compounds, so long as they are not sequential or double move pieces.

So Quintessential Chess is one new CV using 17th century Centurion/Squirrel, and there are 19th C. games with Squirrel for a continual line of succession.

ChessV now supports this game. Since some rules are not known exactly, I had to make some guesses based on information on this page. So here you have it:

Castling: Castling is allowed if neither piece has moved previously. The King always slides 3 squares when castling to either side. The King may not castle into or through Check, but there is no prohibition against castling out of Check.

King's Leap: The King may also make a single 2-space leap horizontally or vertically on its first move. You may not leap into Check, but may leap out of it. Attacks on the square jumped over are irrelevant.

Misc: The special 2-space pawn move restriction mentioned here is implemented. Stalemate and 3-time repetition are considered draws. The 50-move pawn rule is also in effect.