The scene is the first of the third Act. Here Ventidius says:
Caesar and Antony have ever won
More in their officer than person: Sossius,
One of my place in Syria, his lieutenant,
For quick accumulation of renown,
Which he achieved by the minute, lost his favour.
Plutarch (North, sec. 19) says that 'Sossius, one of Antonius'
lieutenants in Syria, did notable good service,' but I cannot find in
him the further statement that Sossius lost Antony's favour. I presume
it is Shakespeare's invention, but I call attention to it on the bare
chance that it may be found elsewhere than in Plutarch, when it would
point to Shakespeare's use of a second authority.