Frank Miller has yet to finish work on Xerxes, his long-discussed follow-up to 300, meaning Dark Horse won't be able to release the comic in time for the March-premiering 300: Rise of an Empire.

What's more, ICv2.com reports no progress has been made on the planned five-issue (previously six-issue) miniseries since March 2011, when Dark Horse CEO Mike Richardson told the website Miller had completed the second issue.

With the 2007 release of director Zack Snyder's 300, sales of the collected edition soared, propelling the 1998 book to the top of bestseller lists and leading Dark Horse to order two 50,000-copy printings to meet demand.

While Snyder's film was a direct adaptation of the comic by Miller and Lynn Varley, even replicating its imagery, it's unclear how close Rise of an Empire hews to the plot of Xerxes, which the writer had described as "a sweeping tale with gods of monsters" centering on the Battle of Artemisium (it's a naval engagement that occurred at the same time as the Battle of Thermopylae).

"This is a more complex story," Miller said in 2010. "The story is so much larger. The Spartans in 300 were being enclosed by the page as the world got smaller. This story has truly vast subjects. The Athenian naval fleet, for instance, is a massive artistic undertaking and it dwarfed by the Persian fleet, which is also shown in this story. The story has elements of espionage, too, and it’s a sweeping tale with gods and warriors.”

ICv2 notes that Miller, who's co-directing Sin City: A Dame to Kill For, "has every intention of returning to the remaining Xerxes issues when his Hollywood commitments are complete."