As is well known, Caesar’s speech that “Cowards die many times before their deaths” was hinted at in North’s Plutarch’s Lives. But previously, it was believed that Shakespeare took that hint and then refashioned it himself with many new details. Yet, as we see both above and below, the specific words and notions of the dramatist’s seemingly original speech actually derive from similar ideas expressed in North’s Dial. In other words, the playwright, when following Plutarch’s description on the ominous dreams of Caesar’s wife, Calpurnia, and coming across a suggestion about Caesar’s brash refusal to fear death, was able to recall a fuller treatment on valiantly facing death in North’s Dial and so added the latter to the tragedy. As shown, this same discussion in The Dial was also the genesis for a line in 1 Henry IV.
EEBO confirms North’s translation is the inspiration for the the doomed emperor’s speech. When we search the database for any works that similarly groups coward (or cowards or cowardly), before, and valiant–as well as taste and death in the same order results only in North’s Dial and Shakespeare’s Julius Caesar.
Yet when writing Julius Caesar, the playwright did not have North’s Dial open in front of him but his Plutarch’s Lives, and it is the latter work that indicated Caesar did indeed make a comment about facing death: “[Caesar] said it was better to die once than always to be afraid of death.” But that is all Plutarch mentions about the matter. Evidently, when the playwright read this, it reminded him of the fuller treatment of the “die but once” passages in North’s Dial. The following table reveals the extensive reliance on North in Julius Caesar 2.2, and it includes a conflation of his passages that appeared in two different texts. The passage shaded in tan, orange, and yellow was based on North’s Dial; the rest, unshaded with shared words in red, comes from his Plutarch:
Finally, as the first table indicates, North’s passage in The Dial also influenced more than just Julius Caesar’s audacious comment; its line “thou owest one death to the Gods” is also the inspiration for Prince Hal’s line, “thou owest God a death” in 1 Henry IV. This cannot be dismissed a coincidence. As shown below, only one work other than North’s Dial and 1 Henry IV juxtaposes “thou owest” with God(s) and death, but this tract would not appear until 1684 and is not making the same point.
As we shall see in later posts, the playwright repeatedly turned to these same pages of The Dial (which comprise a death-bed exchange between the dying Marcus Aurelius and his secretary Panutius) when relating other famous passages on mortality –including Hamlet’s in Hamlet, Prospero’s in The Tempest, and the Vincent-Claudio exchange in Measure from Measure.
 An EEBO search for Coward* PRE/10 before PRE/10 valiant AND taste PRE/10 death yields no results other than North’s Dial of Princes and Julius Caesar.