We know of them mainly, but not entirely, from Tertullian, and the _de Civitate Dei_ of St. Augustine.[323] These scholarly theologians, wishing to show up the absurdity of the heathen religions, found a mine of material in the great work of Varro on the Roman religious antiquities; and though they found him by no means so elegant a writer as Cicero, they studied him with pains, and have incidentally added immensely to our knowledge both of Varro himself and of the Roman religion. St. Augustine tells us that it was in the last three books of his work that Varro treated of the Roman deities, and that he divided them under the heads of _di certi_, _di incerti_, and _di selecti_. In the first of these he dealt chiefly with those with which we are now concerned: they were _certi_ because their names expressed their supposed activity quite clearly.[324] We know for certain that Varro found these names in the books of the pontifices, and that they were there called Indigitamenta:[325] a word which has been variously interpreted, and has been the subject of much learned disputation. I believe with Wissowa that it means "forms of invocation," _i.e._ the correct names by which gods should be addressed. Thus these lists of names come down to us at third hand: Varro took them from the pontifical books, and the Christian fathers took them from Varro. It is obvious that this being the case they need very careful critical examination; and till recently they were accepted in full without hesitation, and without reflection on such questions as, _e.g._, whether they are psychologically probable, or whether they can be paralleled from the religious experience of other peoples. Some preliminary critical attempts were made about fifty years ago in this direction,[326] but the first thoroughgoing examination of the subject was published by R. Peter in the article "Indigitamenta" in Roscher's _Mythological Lexicon_. This most industrious scholar, though his interpretation of the word Indigitamenta is probably erroneous,[327] was the first to reach the definite conclusion that the lists are not really primitive, and do not, as we have them, represent primitive religious thought. It was after a very careful study of this article, which is long enough to fill a small volume, that I wrote in my _Roman Festivals_ of the Indigitamenta as "based on"--not actually representing, I might have added--"old ideas of divine agency, now systematised by something like scientific terminology and ordered classification by skilled legal theologians"; and as "an artificial priestly exaggeration of a primitive tendency to see a world of nameless spirits surrounding and influencing all human life."[328]