Imperial Coins - Images Chosen For The Reverse

I may have found part of the answer. The ancient character of Aeneas is linked with the founding of Rome..... there may also have been an omen of a sow and piglets signifying the supremacy of Rome over the Etruscans..... Of course this could be a complete red-herring?

I assume he's talking about coins like this one; the inscription is simply IMP XIX.

It seems to be part of a three-coin series, all struck in the year IMP XIX (78 AD); the other two have a modius full of grain and a goatherd milking a goat.

I don't think they're meant to symbolize anything from Graeco-Roman mythology; especially with the date featured prominently, I think it's much more a "here and now" thing. All three images speak to me of the simple life made possible by an Empire at peace, with abundance and prosperity in the land. The introductory chapters of Sear simply mention the existence of the pig and goat coins as "animal types", noting that the Flavian dynasty tended to favour such "classical" coin imagery, rather than the purely triumphalistic propaganda of their predecessors (with the JUDAEA CAPTA coins a notable exception).