This is a date found in the Acta Fratrum Arvalium. The text reads XV(...) ob imperium Caes..s divi f... Domitiani Aug..., where XVIII is the earliest possible date.
"Trajan was, in fact, quite active in Egypt. Separate scenes of Domitian and Trajan making offerings to the gods appear on reliefs on the propylon of the Temple of Hathor at Dendera. There are cartouches of Domitian and Trajan on the column shafts of the Temple of Knum at Esna, and on the exterior a frieze text mentions Domitian, Trajan, and Hadrian" Stadter, Philip A.; Stockt, L. Van der (2002). Sage and Emperor: Plutarch, Greek Intellectuals, and Roman Power in the Time of Trajan (98–117 A.D.). Leuven University Press. p. 75. ISBN978-90-5867-239-1.
Salmon, Edward Togo (1936). "Trajan's Conquest of Dacia". Transactions and Proceedings of the American Philological Association. 67: 83–105. doi:10.2307/283229. JSTOR283229.
Last, Hugh (1948). "On the Flavian Reliefs from the Palazzo della Cancelleria". The Journal of Roman Studies. 38 (1–2): 9–14. doi:10.2307/298163. JSTOR298163. S2CID250352207.
Salmon, Edward Togo (1936). "Trajan's Conquest of Dacia". Transactions and Proceedings of the American Philological Association. 67: 83–105. doi:10.2307/283229. JSTOR283229.
Last, Hugh (1948). "On the Flavian Reliefs from the Palazzo della Cancelleria". The Journal of Roman Studies. 38 (1–2): 9–14. doi:10.2307/298163. JSTOR298163. S2CID250352207.
Smallwood, E.M. (1956). "'Domitian's attitude towards the Jews and Judaism". Classical Philology. 51: 1–13. doi:10.1086/363978. S2CID161356789.
Last, Hugh (1948). "On the Flavian Reliefs from the Palazzo della Cancelleria". The Journal of Roman Studies. 38 (1–2): 9–14. doi:10.2307/298163. JSTOR298163. S2CID250352207.