Read the passage about the volcanic eruption at Pompeii.
A cloud . . . was ascending, the appearance of which I cannot give you a more exact description of than by likening it to that of a pine tree, for it shot up to a great height in the form of a very tall trunk, which spread itself out at the top into a sort of branches.
–Letter to Cornelius Tacitus, Pliny the Younger
Why is the passage a primary source?
It includes an interpretation by a historian.
It was written by a well-respected historian.
It includes a detailed description of the event.
It was written by someone who witnessed the event.