Whether intentional or not, the clock is an example of an anachronism. This technique is the inclusion of something that appears to be in the wrong time, used as a device or simply a literary mistake.

Cassius claims that "the clock hath stricken three", signifying the end of the conspirators' meeting about the upcoming assassination. In the Roman era, mechanical clocks were not invented, and the time was told by much more primitive methods.

This anachronism may have been included as subtle humour, or is more symbolic; it may possibly reference the impending 'strike' on Caesar's reign. Furthermore, the motion of the clock is more dramatic than telling time with a sundial etc.

Shakespeare's use of anachronisms throughout Julius Caesar is most likely intentional, but nevertheless it enhances the drama of the conspirator's conversation.