Joseph Poon devotes a monograph, based on his PhD thesis, to identifying the land and sea beasts in Revelation 13. Poon makes creative use of the tripartite structures identified by Georges Dumezil to explain how the dragon, the sea beast, and the land beast form a triad. 

Dumezil identifies “three social-religious functions” in “four mythological traditions including the Indic, the Iranian, the Scandinavian and the Roman” (116). At the top of the hierarchy is the sovereign, representing “both the juridical and supernatural dimensions” and typically “represented by a pair of gods.” The second function “concerns physical prowess and thus is represented by warlike figures,” while the last “governs physical well-being, fecundity and economic productivity and is normally represented by a pair of divinities” (116-7). Poon examines the shifting Roman formulations of this triad, which begins as “Jupiter-Mars-Quirinus” and settles into “Jupiter-Juno-Minerva” (116-129). He argues, with some plausibility, that the three enemies of Revelation 12-13 fit this scheme.

Moving from this to identifying the historical targets of the two beasts, Poon makes a few missteps. He's aware of the questions that have been raised about dating the Apocalypse to the reign of Domitians (153-4) but still opts for that later date. As a result, he misses the specific imperial context of the book, despite the fact that he takes 666 as a Hebrew gematria for “Nero Caesar” (141-4). 

Because of this dating, the destruction of Jerusalem is not within the scope of Poon's reading (though cf. 130-3). He assembles the evidence for seeing the land beast as an imperial priestly figure (157-66). The “priestly” part is true enough, but the meta-symbolism of sea/Gentiles and land/Israel suggests that the land beast is a Jewish rather than a Roman figure. I suspect that John was aware of the imperial priestly resonances of the description, and effectively presents the Jewish high priest as little more than an imperial functionary.

Poon's book is packed with intriguing detail, but, in my opinion, he's mistaken about the historical setting of the book, and so mistaken about the characters and institutions figured by the beasts.