Opus Majus

It was written in Medieval Latin, at the request of Pope Clement IV, to explain the work that Bacon had undertaken.

The 878-page treatise ranges over all aspects of natural science, from grammar and logic to mathematics, physics, and philosophy.

As a recent paper emphasizes, this major work cannot be usefully read exclusively in the context of the history of science and philosophy while forgetting to consider Bacon's religious commitment to the Franciscan Order.

"His Opus maius was a plea for reform addressed to the supreme spiritual head of the Christian faith, written against a background of apocalyptic expectation and informed by the driving concerns of the friars.

It was designed to improve training for missionaries and to provide new skills to be employed in the defence of the Christian world against the enmity of non-Christians and of the Antichrist".