That he ordered a Church to be built at Mambre
Such was the principal sacred edifices erected by the emperor's command. But having heard that the self-same Saviour who erewhile had appeared on earth had in ages long since past afforded a manifestation of his Divine presence to holy men of Palestine near the oak of Mambre, he ordered that a house of prayer should be built there also in honor of the God who had thus appeared. Accordingly the imperial commission was transmitted to the provincial governors by letters addressed to them individually, enjoining a speedy completion of the appointed work. He sent moreover to the writer of this history an eloquent admonition, a copy of which I think it well to insert in the present work, in order to convey a just idea of his pious diligence and zeal. To express, then, his displeasure at the evil practices which he had heard were usual in the place just referred to, he addressed me in the following terms.
Source: Life of Constantine (New Advent)