This church preserves, in its very materials, the sign-manual of an anterior civilization; for its stones came from a Roman temple which stood on the same site.
Issoudun, therefore, according to the researches of this antiquary, like other cities of France whose ancient or modern autonym ends in "Dun" ("dunum") bears in its very name the certificate of an autochthonous existence.

The word "Dun," the appanage of all dignity consecrated by Druidical worship, proves a religious and military settlement of the Celts.

Beneath the Dun of the Gauls must have lain the Roman temple to Isis.

From that comes, according to Chaumon, the name of the city, Issous-Dun,--"Is" being the abbreviation of "Isis." Richard Coeur-de-lion undoubtedly built the famous tower (in which he coined money) above the basilica of the fifth century,--the third monument of the third religion of this ancient town.

He used the church as a necessary foundation, or stay, for the raising of the rampart; and he preserved it by covering it with feudal fortifications as with a mantle.