and unfortunately Croatian coat of arms for this period can not be chessboard despite our great attachment to it. there are theories that chessboard was invented by Petar Krešimir IV in 11th century but there is no any evidence for that. first chessboard as coats of arms of kingdom appear in second half of 15th century.
in fact only "evidence" is this 11th century relief from Split cathedral baptistery.
http://www.vrilo-mudrosti.hr/razno/v...ca%20split.jpg
some claim to see chessboards on falcons wings. I personally don't because this is a bit rough carvings, but i guess you can see anything if you really want to.
said that i will use chessboards on some units shields and flags. Chessboard motif was used often by Normans and others so it wont be "out of time".
the oldest known Croatian coat of arms: a golden six-pointed star (representing the morning star) over a silver moon on a red shield.
this is from 13th century. András II (later Hungarian king)was at the time
"herceg of Croatia" Andreas Dux Croatiae. and we have coats of arms his coins.
unlike the coat of arms we have a pretty decent idea how crown looked like since we have this 11th century relief from Split cathedral which shows Croatian king:
decent modern reconstruction of how crown looked like:
http://croatia.org/crown/content_ima...a_zvonimir.jpg
PS
pleter or to be more exact "troplet" around borders of shield would be a nice authentic decoration.