This was read to me 1968-70ish. Bigger than A4 sized beautifully illustrated hardcover book, with one “chapter” and picture per two pages. British published as I was in New Zealand. The stories of Helen of Troy, Paris, Achilles, and Ulysses were there.
Stump the Bookseller
New format, same book stumper solving.
Possibly ‘Tales of the Greeks and Trojans’ by Roger Lancelyn Green and illustrated by Janet and Anne Grahame Johnstone (Paulton [England] Purnell [1964], ©1963.).
The format is similar to your description – each story on a two page spread but with two illustrations. If you search google images for the title and Grahame Johnstone, you’ll find quite a few interior spreads.