Hello! A lot of the Roman rings I post could probably be worn by both men and women, depending on their time period.
Early in Roman history, men’s rings were mostly forged from iron and meant to be used as personal seals (source 1: Lacus Curtius). As time went on, Rome became exposed to new art forms and new materials through warfare and diplomacy. Gold and silver became options instead of iron.
Perhaps as a reaction against the influx of gold and silver, or perhaps to express political views, some late Republican men wore iron rings in order to express the austerity and simplicity associated with the early period. (source 1). Apparently Gaius Marius (157-86 BCE) only wore iron rings and never gold ones for this reason (source 1, from Pliny).
However, for a time in Roman history, only elite senators, magistrates, and equites could wear gold rings under the ius annuli aurei, or the right of the gold ring, so perhaps most upper-class men actually flaunted their ability to wear gold rings in order to express their status.
In the early empire, Augustus (r. 27 BCE-14 CE) granted the right to wear gold rings onto his favorites, but Tiberius (r. 14-37 CE) restricted the wearing of gold rings to those whose ancestors had had enough property (source 1). Septimius Severus (r. 193-211 CE) later granted his soldiers the right to wear gold rings, with freedmen and slaves permitted only silver or iron rings (source 2: Encyclopedia Britannica 1911). Under Justinian (r. 527-565 CE), all free male citizens were granted the right to wear gold rings, the law by then mostly abandoned (source 2). Thus the wearing of gold rings expressed different statuses over time, and men no doubt were eager to show off their social standing by wearing gold rings at times when it served their interests to do so.
Roman men also didn’t seem to have an issue wearing gemstones. Sulla (139-78 BCE) apparently wore a ring with an intaglio depicting the defeat of Jugurtha, and Augustus used an intaglio seal ring first with a sphinx and then with the head of Alexander the Great (source 1, both from Pliny). Roman intaglios are most always colorful, either made of glass or natural gemstone.
Certain rings were probably only worn by men, such as army rings. Here’s a silver ring that was made for a member of the I Italica, depicting a soldier with a shield, dated to the 1st to 2nd centuries CE. Here’s another ring that was made for a member of the II Traiana Fortis, engraved with the name of the legion, dated to the 2nd century CE. Finally, here is a silver ring with a carnelian intaglio dated to the 2nd to 3rd centuries CE that was made for a member of the XI Claudia, proving that both men and women would wear gemstones and intaglio rings. It’s interesting to note that all these rings are made out of silver, rather than gold, likely because these rings were constructed before it was permissible for soldiers to wear gold, and perhaps also because gold was simply more expensive to acquire.
Ultimately, I think that some believed Roman men should be constricted not by which jewelry they could or could not wear, but by how much. Roman men certainly wore rings, but Quintilian, a 1st century CE rhetorician, advised aspiring orators that “the hand should not be overloaded with rings, which should under no circumstances encroach upon the middle joint of the finger” (source 3: Quintilian, Institutia Oratoria IX.3.142, via Lacus Curtius). To be a successful orator, according to Quintilian, the less rings the better. Was this related to a belief that it wasn’t masculine to wear so much jewelry? Perhaps. But the fact that Quintilian had to specifically point out ring wearing implies that Roman men were in fact wearing lots of rings, at least at this point in the empire.