One of the most common coin types from the ancient world depicts a guy falling off a horse and getting stabbed surrounded by the legend "FEL TEMP REPARATIO," meaning "the return of fortunate times." Since the stabber was a Roman soldier and the stabbee clearly a barbarian (note the "Phrygian Cap" on the fallen figure on the two larger coins, marking him as foreign), it was the Imperial government's statement that "no seriously, we're properly dealing with invaders this time." I kind of wonder if these coins raised a lot of questions already answered by the coins.
These coins were part of a coinage reform made under the joint rule of Constantius II and Constans I, Constantine's younger two sons (he put his eldest, Crispus, to death, and the next oldest, Constantine II, tried to conquer Constans' territory and died in the process) in around 340. There seemed to have been at least three bronze or heavily debased silver coins at first, all of which are in the top row. Our sources mention denominations called the "centenionalis" and "pecunia maiorina" around this time, but it's not clear which specific coins they're referring to.1 The third coin contains the same message on the reverse, though it depicts the emperor standing on a galley, holding a globe representing the world on which there is a phoenix, probably reinforcing the idea of a restoration of strength from the ashes of bad days, and the emperor's other hand holding a standard with a symbol of Christianity. The far right coin has a reverse where two personifications of victory hold wreaths together, and around them a legend meaning roughly "the victory of our lords and emperors."
But while that falling horseman design is common on coins, you rarely see examples as big as those first two coins of mine. Like so many other times in history, the imperial government dealt with financial shortfalls by shrinking their coins and reducing silver content. The bottom two coins are probably the same denomination as those big ones, just from a few years later. And as you might expect, those two smaller denominations in the first row quickly stopped being made as inflation and shrinking horseman coins made them kind of useless. While they stopped making this reverse design after Constantius II's reign, it's not clear which, if any, bronze coins were continuations of the same denomination or new denominations. 4th Roman century coinage has a lot of mysteries and ambiguities.
One other thing is that I think this picture is a good place to talk about how much the images on hand carved dies could vary. All but that rightmost coin with the victories on it depicts the same man, Constantius II, with that final one depicting Constans I. But by this point, imperial portraiture was more concerned with depicting "the emperor" than the specific person on the throne, so portraits of those two brothers basically look identical. But look at the two big coins in particular. If I didn't know about this, I would have assumed those were supposed to be two different guys. What you're seeing is the difference between how a die carver in Constantinople and one in Thessalonica carved the same portrait. Different mints have different house styles, and those who really get into a period of Roman coinage can often tell at a glance where a coin was made just by the portrait. I can do that myself a little bit for coins of Diocletian's tetrarchy, and I might make a post with more detail about that later.
I also want to point out that I'm not sure that bottom left coin is an official issue. The proportions on Constantius' face make it look almost like a Moai head to me, and I haven't seen any other that quite looks like that. It could just be that a new guy at the mint carved it weird, but we do know that there were some "barbarous" copies of coins of this period, probably made unofficially to deal with local coin shortages, something I talked more about here.
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"Pecunia maiorina" just means "big coin," and our only reference to them comes from Constantius II declaring them demonetized in 354. This may refer to the earlier, bigger falling horsemen coins, but it could also refer to the larger coins the usurper Magnentius minted, or it could refer to the older coins of Diocletian and his tetrarchy. It could even be a general descriptor rather than a specific denomination and referred to more than one of those. It's a very ambiguous passage.