Before Spartacus and the rebels leave to attack the brothel, Crixus tells him that it's not his fight. To which Spartacus replied, "I gave my word; blood and honor. It yet speaks to the man." These are the very same words he shared with Sura in "The Red Serpent" before leaving for war.
The Dagger that Spartacus looted from one of the corpses in the very first scene, was depicted with the same prop that was used as the Thracian dagger bought by Numerius in "Blood & Sand." From then on, Spartacus can be seen wielding it on his shoulder hilt.
Wentworth Miller was in talks to take over the title role of Spartacus from Andy Whitfield, when Andy Whitfield left the series due to health problems. But, the role went to Liam McIntyre.
The character Donar is introduced in the first episode. His backstory being that he was one of the escaped gladiators from Batiatus' ludus; though viewers did not meet the man in the first season. Equally, the gladiator Liscus the Gaul is finally shown, as he'd only ever been mentioned by name in the first season.