They will play Julius Caesar and Marcus Crassus respectively.
Lasance is known for his role as Ben McMahon in the Australian legal drama "Crownies," as well as for playing Quick Lamb in the TV miniseries "Cloudstreet."
Merrells played DO Griggs in the U.K. drama "London's Burning," had a recurring role in the BBC crime drama "Mersey Beat," and was also seen on "Family Affair" and "Doctors." He was last seen on the big-screen in "The Wolfman."
Liam McIntyre plays the title role of Spartacus in the series, which is now in its third season.