Caesar is dead. So long live HBO and the second season of “Rome,” the extravagantly expensive series returning this Sunday whose vision of the world’s most notorious empire alternates between “Blade Runner”-ish working-class chaos and quarrelsome emperors, witchy women, and quibbling upper-class families whose foul mouths wouldn’t be out of place in one of the more decadent precincts of contemporary London. (“Rome” is one of those joint HBO/BBC series whose American imprint tends to get buried under the British one. “Look chaps, we know empires,” you can imagine the Brits telling their American counterparts. “Leave it to us.”)

Caesar is not only dead, but, better, dramatically expendable. After all, the power struggle between the sensualist Mark Antony, played by James Purefoy in the manner of a sly, vulgar Richard Burton, and the precociously cerebral Gaius Octavian (Max Pirkis), soon to become the slightly older Octavian (Simon Woods), is light years more interesting than that between stately old Caesar and fraying, decrepit Pompey.

Cleopatra (Lyndsey Marshal) is also back, come to pay her respects in Episode 2 to Antony, who would appear to have inherited Caesar’s mantle after Brutus and his fellow assassins are unable to seize power. Cleopatra’s first meeting (at a dinner party) with Antony’s cat-eyed mistress, Atia of the Julii (Polly Walker), fully lives up to its splendidly catty promise. Though dismissing her Egyptian rival as a “mouse,” Atia seems preternaturally aware that her grand love affair with the Roman proconsul is destined to be superseded in the annals of history and literature. There will be no Shakespeare play — and the most exuberantly cinematic of all Shakespeare plays, at that — titled “Antony and Atia.”

Not that Atia is suffering from a slackening of Antony’s amatory attentions. Sleeping in on the day of his speech at Caesar’s funeral, he stretches languorously on his back, notes a group of black-clad women hovering nearby, of whom one is Atia, and announces, in blunt terms, that making love to a woman dressed in funeral clothes is one of the few sexual achievements he has yet to make his own. “Nor shall you, then,” Atia fires back. “That’s a shame,” Antony replies, sticking to his guns. “I am not rising from this bed until….” Well, let’s just say that “Rome” *is* on HBO and takes full advantage of the fact. (The version shown on BBC suffered a certain amount of censorship.) “Fine, fine,” says the ever pliable Atia, who tolerates Antony’s flings so long as they’re not with someone who outranks her socially (i.e., Cleopatra). “Fetch that German slut in the kitchen,” she orders a flunky.

As with the opening episodes of most second seasons, there’s a fair amount of mopping up and sorting out to do after the climactic end of the first season, including the ignominious departure from Rome by Brutus and his cohorts. Lucius Vorenus (Kevin McKidd, bearing a marked resemblance to the new James Bond while possessing not an ounce of his cool) and Titus Pullo (Ray Stevenson, thuggish looking but disarmingly sensitive) are back as the soldier buddies who can’t stop arguing with each other, mainly because Vorenus, a priggish, straight-arrow centurion, can never see the wood for the trees of military regulations and etiquette.

And now that Caesar is dead (which is partly Vorenus’s fault) and Vorenus’s wife is dead (which is mostly Vorenus’s fault) and Vorenus’s children have fled (which is entirely Vorenus’s fault), Vorenus has, perhaps understandably, started to go stark raving bonkers, testing even Pullo’s genius for friendship and ability to smooth troubled waters. Few things are more frightening than a guilt-ridden Roman centurion with a sword in his hand and the rage of Hades in his soul, and the tone of this opening episode can be very dark indeed.

As in the first season, “Rome” ricochets constantly between the upper-class world of Atia — whose sumptuous home plays roughly the same role here as “The Planet” café does on Showtime’s “The L Word,” with at least as much sex and definitely superior conversation — and the grubby back alleys in which soldiers, merchants, prostitutes, and mercenaries live side-by-side, and where despised foreigners from the empire’s outposts are a major demographic presence. The back-and-forth between the two spheres becomes predictable after awhile, but there’s no doubt that “Rome” delivers on at least some of the promise of a serial 19th-century novel — a sprawling, cross-section view of society laid bare like an ant farm, intelligently explained and lovingly delineated. If one has a gripe, it’s that scenes that ought really to go on longer, to be more novelistic, are often are prematurely cut short, as if in fear of viewer boredom, while purely expository scenes are given more screen time than needed.

If “The Sopranos,” “Deadwood,” and other HBO hit series, not to mention the peculiar goings-on documented in “Curb Your Enthusiasm,” can return year after year, you’d think, as a subject, the Roman Empire could keep “Rome” afloat for at least two decades. But this second season will also be its last, a sign, perhaps, that the series has not been the critical and popular success originally hoped for. Well, it’s true, the program has some daunting historic competition, on the page, stage, and screen, but there’s enough that’s fresh here — particularly the troubled friendship between Vorenus and Pullo — to have made the series worth it.

In the figure of Octavian, we also have a fascinating interpretation of a contemporary phenomenon, namely the born politician. Unlike that born emperor, Antony, who can’t be bothered with the minutiae of governance, Octavian is a cold, conniving, highly intelligent administrator for whom the minutiae mean everything. In the second season the emperor and politician go mano-a-mano (at one point literally), and there’s no prize for guessing who comes out on top.

bbernhard@nysun.com