In study, a first-hand account is commonly known as a primary source.
They are a firsthand account by a slave.
Primary source
I believe what you are describing is called a primary source.
The Coliseum is pretty much proof itself that games and races were held. The are also many ancient documentions that account for chariot races firsthand.
Thucydides was a general for a short part of the Peloponnesian War and recorded a history of the first two thirds of that war.
they are a firsthand account by a slave
He or she is actually called the narrator. The narrator differs from the author in that the author wrote the poem but the narrator lives inside the poem and is giving a firsthand account of the story.
Primary Source
Firsthand: obtained by, coming from, or being direct personal observation or experience "a firsthand account of the war"
primary source
They are a firsthand account by a slave.
primary
Primary source
Primary source
Yes, he did. See a firsthand account in this linked page.
they are a firsthand account by a slave
shes giving a firsthand account of her experience