I hope someone can settle this - for determining mint dates, is Vespasian's first year (69AD) counted as COS I, or is the start of his second year (70AD) considered COS I? I've seen listed mint dates saying both.
Thank you for that - did he not assume COS II in 69 because he wasn't in Rome yet? I hope these aren't too elementary questions, but I'm just curious.
Consulships were not necessarily related to being emperor. Many emperors had been Consul before they were emperor so their first coins were dated COS. Several took a second Consulship beginning the first January they were emperor. Vespasian did this in 70 with coins dated COS II so COS coins with no numeral should be 69 AD. Where Vespasian was a bit unusual is that he assumed another consulship each year except for 73 and 78 so many of his coins can be year dated by the COS number. More common, for example was the case of Trajan who only took a total of six consulships, one before he was emperor and five more scattered in his 21 years as emperor. That means a Trajan coin dated COS V could be any time between 103 and 111 and COS VI from 112 to his death. IMHO all Roman Imperial collectors should own one of the old fashion Sear single volume Roman Coins and their Values for the titles charts he placed at the start of each reign. David told you that Vespasian was first Consul in 51 and you won't find this in Sear. He was not Consul in 69 but he had been previously so he could include this in inscriptions. https://en.wikipedia.org/wiki/List_of_Roman_consuls The list above gives the Consuls for each year. Under 51 AD you will find that Vespasian only served as Consul in November and December. If a Consul did not finish his year and he would be replaced by a Consul Suffectus. It was a greater honor to be Consul from the start but being a suffectus was the common way to honor men after the emperor had placed his name of the year at the start. Note in 72, Trajan was a suffectus replacing Vespasian. Scanning over that list will reveal quite a few names of interest.
Dating is more often by TRP number, which when used, changed yearly (Dec. 10 in the early empire). For example, Hadrian Was "COS " in 117, "COS II" in 118, but stayed "COS III" from 119-138, so COS numbers can't help in those years. But his TRP numbers changed each year and they do pin it down to a particular year. If you can find an older one-volume Sear (2nd, 3rd, or 4th edition all work) he has the dates of TRP numbers, COS numbers and other titles for each emperor. I cannot fathom why this useful information was omitted from the five-volume version.
Vespasian assumed his second consulship on 1 January 70, presumably while he was still in Alexandria. He did not arrive in Rome until October of 70.
By the time of the Empire, I am unclear on what were the duties and powers of the Consuls other than 'as the Augustus directs'. The Emperors started out giving lip service to the Republican values and maintained the offices but there should be no question that the Emperor was king in every way but name. Being in Rome was not necessary if the Emperor wanted a Consulship. In many senses, 'Rome' was where the Emperor was.
And further evidence of the Republican values sham - Vespasian dated the start of his reign on 1 July 69 when the legions in Alexandria declared for him. No need for the Senate's permission!