Gildas wrote his main work, the 'Ruin of Britain', about 540 A.D. or just before, when he was forty three years old (26.1).

Historical introduction.

'There was a prophet of the people in the time of the Britons called Gildas. . . .'

Preface.

In this letter I shall deplore rather than denounce; my style may be worthless, but my intentions are kindly.

The ruin of Britain.

In hac epistola quicquid deflendo potius quam declamando, vili licet stilo, tanem benigno, fuero prospecutus, ne quis me affectu cunctos spernentis omnibusve melioris, quippe qui commune bonorum dispendium malorumque cumulum lacrimosis querelis defleam, sed condolentis patriae, incommonditatibus miseriisque eius ac remediis condelectantis edicturum putet.

De excidio britonum.