15 years old card game with ancient battles theme and complex mechanics
Ok, after the comment about "Battle Line" (Thanks to @user30903) I started to view the game description and suddenly I saw a war unit called hoplite... and then I recalled.

The PC game is called "Hoplites". It is completely free and its manual is available here. It is based on a board game called SPQR. The game "Battle Line" is from the same company.