Publius Servilius Casca Longus, Roman tribune in 43 B.C., is the name of the assassin who first struck Julius Caesar on the Ides of March, in 44 B.C. The symbol to strike came when Lucius Tilius Cimber grabbed Caesar's toga and pulled it from his neck. A nervous Casca then stabbed the dictator, but only managed to graze him around the neck or shoulder.
Publius Servilius Casca Longus, as well as his brother who was also a Casca, were among the conspirators who killed themselves in 42 B.C. This honorably Roman manner of death came after the Battle at Philippi, in which the forces of the assassins (known as the Republicans) lost to those of Mark Antony and Octavian (Augustus Caesar).
Here are some passages from ancient historians that describe the role Casca played in the assassination of Caesar and inspired Shakespeare's version of the event.
"82 As he took his seat, the conspirators gathered about him as if to pay their respects, and straightway Tillius Cimber, who had assumed the lead, came nearer as though to ask something; and when Caesar with a gesture put him off to another time, Cimber caught his toga by both shoulders; then as Caesar cried, "Why, this is violence!" one of the Cascas stabbed him from one side just below the throat. 2 Caesar caught Casca's arm and ran it through with his stylus, but as he tried to leap to his feet, he was stopped by another wound."
"66.6 But when, after taking his seat, Caesar continued to repulse their petitions, and, as they pressed upon him with greater importunity, began to show anger towards one and another of them, Tullius seized his toga with both hands and pulled it down from his neck. This was the signal for the assault. 7 It was Casca who gave him the first blow with his dagger, in the neck, not a mortal wound, nor even a deep one, for which he was too much confused, as was natural at the beginning of a deed of great daring; so that Caesar turned about, grasped the knife, and held it fast. At almost the same instant both cried out, the smitten man in Latin: 'Accursed Casca, what does thou?' and the smiter, in Greek, to his brother: 'Brother, help!'"
Although in Plutarch's version, Casca is fluent in Greek and reverts to it in a time of stress, Casca, well known from his appearance in Shakespeare's Julius Caesar, says (in Act I. Scene 2) "but, for mine own part, it was Greek to me." The context is that Casca is describing a speech the orator Cicero had delivered.
Nicolaus of Damascus
"First Servilius Casca stabbed him on the left shoulder a little above the collar bone, at which he had aimed but missed through nervousness. Caesar sprang up to defend himself against him, and Casca called to his brother, speaking in Greek in his excitement. The latter obeyed him and drove his sword into Caesar's side."