I'm trying to think of some examples, but the ones I can instantly come up with are not very interesting. Refurbished m16 helmets in Wehrmacht service and Hadrian helmets imported from France for Imperial Army during WWI used in Red Army tier.
Well, there is another interdasting example. The Roman senate actually existed into the 7th century in some passive form:
> It is not known exactly when the Roman senate disappeared in the West, but it appears to have been in the early 7th century, when Rome was under the dominion of the Exarchate of Ravenna. Records that in both 578 and 580, the politically-impotent senate of Rome sent envoys to Constantinople along with pleas for help against the Lombards, who had invaded Italy ten years earlier. Later, in 593, Pope Gregory I would give a sermon in which he bemoaned the almost complete disappearance of the senatorial order and the decline of the prestigious institution,[ suggesting that by this date, the senate had officially ceased to function as a body. Although the Gregorian register of 603 mentions the senate in reference to the acclamation of new statues of Emperor Phocas and Empress Leontia,[ scholars such as Ernst Stein and André Chastagnol have argued that this mention was likely nothing more than a ceremonial flourish. In 630, any remnants of the senate were swept away when the Curia Julia was converted into a church (Sant'Adriano al Foro) by Pope Honorius I.
Rome had population of like 15k people at that point, who the hell were these people and what was their "power"? What did their assemblies look and work like? How did they live in a city of million turned 15k? Very interesting.
Also: according to articles linked here (https://en.wikipedia.org/wiki/Japanese_clans), a ton of Sengoku era clans are sitll alive and well, including the ones you can play in Shogun TW like Oda and Shimazu.