What is clearly justified by the historical sources
In Stanley Kubrick's film of Spartacus, many events that are documented in the historical sources are accurately portrayed. In the film, we see Spartacus and other slaves seize kitchen implements from the cookhouse in which they are eating and attack the guards. This is clearly justified by Plutarch in Fall of the Roman Empire; "seventy-eight, who realised this, managed to act in time and get away, armed with choppers and spits which they seized from some cookhouse".
The film shows that in the summer of 73 BC, "about seventy slaves escaped from Batiatus's training school at Capua and established a defensible position on Mount Vesuvius some thirty kilometres away. " This is clearly justified by the historical sources and is accurately portrayed in the film.
The film also correclty portrays the Cilicians pulling out of an agreement with Spartacus, in which they were going to transport slaves to Sicily. The Cilicians are bribed by the Romans to pull out of the agreement, so that they can quell the slave revolt. This left the slaves trapped near Rhegium in the Peninsula of Brittium, and with armies marching towards them from north and east, Spartacus was left with no choice but to turn and face Crassus...
What is contradicted by the historical sources
In the film, Spartacus says that he was a slave from birth and that his father before him was also a slave. However, this is contradicted by accounts of Spartacus' life. It is said that he had once served with the military service with the Romans and was then later sold as a slave.
The next contradiction is when, in the film, Spartacus leads the slaves to cross the Alps where they would disperse and go to their homes. However, Plutarch claims that the slaves had not agreed with Spartacus' plan: "His men however, would not listen to him. They were strong in numbers and full of confidence, and they went about Italy ravaging everything in their way.1"
One of the most incorrectly portrayed events in the film is when spartacus dies. In the film, Spartacus is crucified after being forced to have a gladiatorial fight with his close friend. However, it is documented that Spartacus actually died in battle, when he ran at Crassus: "Though he did not reach Crassus, he cut down two centurions who fell on him together."
What has been added in
In the film, Spartacus falls in love with a kitchen slave who he takes with him and who eventually has his child. However, none of this is documented in the historical sources and was probably added in to have the seemingly mandatory love interest that is in Hollywood movies.
Along with Spartacus' 'wife' comes Spartacus' baby son who was born shortly before he died. This has been added in by the film makers, probably to give the story an element of happiness in the end because after the birth of Spartacus' son, his blood line is continued even though he is now dead.