Damian Lewis, Saffron Burrows, John Malkovich, Virginie Ledoyen, Darryl Hannah, and Jonathan Rhys Meyer are all attached to appear in the film, scripted by Mia Sperber and Stefano Pratesi.
The film, set at the time of Emperor Charlemagne and inspired by the The Song Of Roland, is due to start shooting in August.
Ruiz is promising battle scenes as well as romantic intrigue. The film will also have contemporary resonance.
The prolific director has recently completed another much smaller budgeted feature, Recta Provincia (Honest Kingdom) shot in his native Chile.
The film, shot on digital, is likely to be unveiled either in the Locarno or Rome Festivals. Produced by Chilean TV, it is set in a remote community in the mountains where folk stories about witches are still believed.
Here in Cannes, Ruiz unveiled a new 3-minute short as part of the Festival's Chacun Son Cinema.
Ruiz's previous film Klimt will be released later this summer by Soda Pictures in the Director's Cut rather than in the producers' version, which was also on offer. Klimt has also secured US distribution through new LA-based distributor Outsider Pictures.