Just finished and, for once, without help from this forum.
Re (pun not thematically intended!) the letters/numbers debate - it never occurred to me to use numbers. Each cell contains letters entered in a thematic way, making the clue answers. In 6 cases this means the clue answer is the same as the number of cells available.
As for the title, I would never have seen the connection between the 1899 and Ares - thank you to whoever pointed that out.