He was assistant librarian of Harvard University from 1856 to 1872, and planned and perfected an alphabetical card catalogue, combining many of the advantages of the ordinary dictionary catalogues with the grouping of the minor topics under more general heads, which is characteristic of a systematic catalogue.
Wagner's retouching of Gluck's Iphigenie en Aulide and his edition of Palestrina's Stabat Mater demand mention as important services to music, by no means to be classified (as in some catalogues) with the hack-work with which he kept off starvation in Paris.
366-384, the catacombs had begun to be regarded with special devotion, and had become the resort of large bands of pilgrims, for whose guidance catalogues of the chief burial-places and the holy men buried in them were drawn up. Some of these lists are still extant.'
Besides a large number of archaeological papers in periodicals, in the Annali of the Institute of Rome, and in the Transactions of the Berlin Academy, and several illustrated catalogues of Greek, Roman and other antiquities in the Berlin, Naples and Vatican Museums, Gerhard was the author of the following works: Antike Bildwerke (Stuttgart, 1827-1844); Auserlesene griech.
About the 4th century he is treated in the catalogues as two personsAnacletus and Cletus.