[ptjuzjre] 10 deep chess board

We consider a chess variant with 10 ranks (rows).  We leave unspecified the number of files.  Previously, 10 files.

Pawns start on the third rank separated by 4 open ranks from the opposing row of pawns.  Two-square initial pawn move is possible as normal.  The general idea is to preserve the feeling of 8x8 chess as much as possible.

Pieces start on the second rank immediately behind the pawns.  There is a backfield of an empty first rank.  Back rank mates will probably be less common.  Castling might not be necessary.

Or, fill the backfield with more pieces, which may be desirable with a larger board.

Do pawns promote on the 9th rank or 10th?  Or both: a pawn may optionally remain a pawn on the 9th.  If both, when can a pawn on the 9th promote?  Only with movement (to the 10th), or it can promote in place on any subsequent turn?  Having two promotion ranks might be useful if promoting to a colorbound piece, e.g., bishop.

In 8x8 chess, a variant in which a pawn can wait on the 8th rank then promote in place later when the time is right might yield interesting tactics.

This could be extended to even more than 10 ranks: start with a larger backfield.  Inspired by real life where an army can usually retreat an arbitrary amount.