As is the case with anything taken for granted, tantalizingly little is explained of the literary system. We can tell, though, that imitation of Greek models was de rigueur for Roman poets, and that there were kinds of poetry to imitate. From Propertius's remark and from Callimachus's categories, we suspect, too, that the size of a poem was important in generic definition. Moreover, the thematic stress of generic comment hinted sufficiently to Renaissance writers that cultural transfer was achieved by generic means; that Roman authors had so proceeded to domesticate Greek values, and that they might accomplish the same task in the same way.