Where was Mark Antony during Caesar's assassination in Julius Caesar?

If you look carefully at Act III scene 1, we can see that
Mark Antony is carefully removed from the scene by Trebonius before the conspirators
start their action against Caesar, culminating in his assassination. Examining the text,
we see that Cassius fears the discovery of the plot, but then he is reassured by the way
that Trebonius does what he had to do by leaving with Mark
Antony:

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Trebonius knows his time; for look you,
Brutus,

He draws Mark Antony out of the
way.

Thus it is that Mark
Antony, as planned by the conspirators, is absent from the scene when the murder is
committed, and is therefore not present to witness the assassination of his leader. This
of course, as we go on to see, is a decision that backfires disastrously on the
conspirators. The way that Brutus underestimates Mark Antony and ignores the advice of
Cassius to kill him too results in his own downfall.