There remains another striking feature of Celtic religion which has not yet been mentioned, namely the identification of several deities with Apollo. These deities are essentially the presiding deities of certain healing-springs and health-resorts, and the growth of their worship into popularity is a further striking index to the development of religion side by side with certain aspects of civilisation. One of the names of a Celtic Apollo is Borvo (whence Bourbon), the deity of certain hot springs. This name is Indo-European, and was given to the local fountain- god by the Celtic-speaking invaders of Gaul: it simply means 'the Boiler.' Other forms of the name are also found, as Bormo and Bormanus. At Aquae Granni (Aix-la-Chapelle) and elsewhere the name identified with Apollo is Grannos. We find also Mogons, and Mogounus, the patron deity of Moguntiacum (Mainz), and, once or twice, Maponos (the great youth). The essential feature of the Apollo worship was its association in Gallo- Roman civilisation with the idea of healing, an idea which, through the revival of the worship of AEsculapius, affected religious views very strongly in other quarters of the empire. It was in this conception of the gods as the guides of civilisation and the restorers of health, that Celtic religion, in some districts at any rate, shows itself emerging into a measure of light after a long and toilsome progress from the darkness of prehistoric ideas. What Caesar says of the practice of the Gauls of beginning the year with the night rather than with the day, and their ancient belief that they were sprung from Dis, the god of the lower world, is thus typified in their religious history.