Haeberlin, E. J. Aes Grave. Das Schwergeld Roms und Mittelitaliens. (Frankfurt, 1910).
Aes Grave. The main money of Rome and Central Italy.
Available online: http://gallica.bnf.fr/ark:/12148/bpt6k880368k/f1.image
This monumental 1910 study, "Aes Grave, das schwegeld Roms und mittelitaliens" by Ernst Justus Haeberlin consists of two volumes, one with 308 pages of text and one with a very large (13 1/2" x 18") portfolio of 103 plates. This was the first modern work on this series and is still a primary reference (due to the excellent illustrations). Scarce Forni reprints often sell for more than $300. Rare originals sell for more than US $4,000.