In this series, many of the coins are quite common. What you see below is a mule. This coin should have a reverse with COS VIII in the exergue. This coin has COS VI. So, we have a Vespasian obverse and a Titus reverse. During this period Titus was COS VI. So this coin is already a fascinating curiosity. What could make it even more interesting? In a word-rarity. This coin is the second one known. The first known is owned by @David Atherton. His coin is the RIC reference coin. I had seen David's coin before and admired it. I never thought I would have the chance to have one myself. Please post your interesting rarities or curiosities. Vespasian AR Denarius 77-78 CE (18mm 3.17g) Obv: Head laureate left; IMP CAESAR VESPASIANVS AVG Rev: COS VI in exergue; Oxen 2 yoked Purchased from C J Martin coins on Vcoins.