Roman Imperial Coinage II.3: From AD 117 to AD 138 Hadrian by RA Abdy with PF Mittag
Identifying Roman Coins by Reece, R. & James, S.
The London Mint of Constantius & Constantine by Cloke, H. J. & Toone, L.
Roman Coins and their Values, Volume V: The Christian Empire: The Later Constantinian Dynasty and the Houses of Valentinian and Theodosius and their Successors, Constantine II to Zeno, AD 337 - 491 by Sear, D. R.
Roman Coins and their Values, Volume IV: The Tetrarchies and the Rise of the House of Constantine; The Collapse of Paganism and the Triumph of Christianity, Diocletian to Constantine I, AD 284-337. by Sear, D.R.
Roman Coins and Their Values, Volume II: The Accession of Nerva to the Overthrow of the Severan Dynasty AD 96 - AD 235 by Sear, D.R.