According to Christian historians,[2] during the consulship of the Emperor Decius and Vettius Gratus (250 AD), Pope Fabian sent out seven bishops from Rome to Gaul to preach the Gospel: Gatianus to Tours, Trophimus to Arles, Paul to Narbonne, Saturnin to Toulouse, Denis to Paris, Austromoine to Clermont, and Martial to Limoges.

According to the Catholic historian Louis Duchesne (Christian Worship: Its Origin and Evolution), the traditions preserved at Tours furnished Gregory with only the name of Gatianus and perhaps the 50-year extent of his episcopacy; it was by comparison with a brief early biography of Saturninus of Toulouse (Passio S. Saturnini) that Gregory arrived at the date 250 for the beginning of Gatianus' ministry at Tours (History of the Franks, 1.30).

He devoted half a century to evangelization, amid innumerable difficulties, and at his death the diocese of Tours was securely established.

[3] In a part of the empire where Mithraism was a dominating force among the legions, Léon Jaud reports that Gatianus likewise retreated into a grotto and there celebrated a mystical banquet (célébrait les saints mystères), but that of Christianity.

Two grottos cut into the limestone hill above the river Loire, across from Tours at the largely demolished Marmoutier Abbey, are designated the first sites where Gatianus celebrated the liturgy.

...They have been dealt with as the Catholic church deals with most of such places today; polished and furnished up; labelled and ticketed; edited, with notes, in short, like an old book.

The large garden stretched beneath us, blooming with fruit and wine and succulent vegetables, and beyond it flowed the shining river.

With the rise in importance of Paris, Gatianus came to be seen more and more as a disciple of Saint Denis, and is so described at many modern Catholic websites.