In "Dante's Inferno", why does Virgil speak of "false and lying gods?"

The previous post is quite eloquent and also right, but I think that there is an extra element to Virgil's adress of the ancient Greek and Roman Gods as lying. Remember that Dante's Inferno has a strong Biblical theme, and so, naturally, Dante tries so portray Christianity as the one 'true' religion, and what better way to do so than by demeaning the others? The other reason is of course that, like the above post highlighted, the classical ancient Gods were given human like attributes such as greed, lust, wrath and so on.