William Shakespeare's Julius Caesar is based on historical events that occurred some 1600 years earlier. Sources such as Suetonius and Plutarch, writing a century after Caesar's death in 44 BCE, also tell us of a soothsayer who told Caesar to beware of the Ides of March; that Caesar's wife Calpurnia had a terrible dream about her husband being killed; and that Caesar did make some comment to Brutus during the assassination. The ancient sources also tell us that Antony did try to put a crown upon Caesar's head and that he refused the crown. Ancient sources also anticipate Shakespeare in saying that Caesar had epilepsy:
Suetonius tells us that "He was twice attacked by the falling sickness during his campaigns" (Thomas Browne translator), although he says nothing about the attack of this disease that Shakespeare mentions in his play.
Interestingly, Suetonius tells us that several of the assassins were designated in Caesar's will as "guardians of his son, in case one should be born to him" and that Caesar also named in his will "Decimus Brutus even among his heirs in the second degree" (Thomas Browne translator). Antony omits mention of these things in Shakespeare's version of the play. Shakespeare does follow Suetonius, however, in mentioning that Caesar left some of his gardens and a gift of money to each Roman citizen:
To the people he left his gardens near the Tiber for their common use and three hundred sesterces to each man. (Thomas Browne translator)
So, for the most part, Shakespeare does seem to follow the historical sources to a signficant degree. The playwright does, however, seem to make Caesar look like a more sympathetic figure and downplay Caesar's ambition, especially in the funeral speech given by Antony. Suetonius does suggest that certain rumors about Caesar's future plans led the conspirators to act quickly:
....the report had spread in various quarters that he intended to move to Ilium or Alexandria, taking with him the resources of the state, draining Italy by levies, and leaving the charge of the city to his friends; also that at the next meeting of the Senate Lucius Cotta would announce...that inasmuch as it was written in the books of fate that the Parthians could be conquered only by a king, Caesar should be given that title. (Thomas Browne translator)