For direct quotes, I would put "Marcus Aurelius writes..." Any document is treated as though it still reads in the present. That said, you could put "Marcus Aurelius wrote that ..." when paraphrasing and be perfectly fine as well. It's really a stylistic decision.

According to Hamilton College's Writing Center:

"Most historians shift into the present tense when describing or commenting on a book, document, or evidence that still exists and is in front of them (or in their mind) as they write. ("de Beauvoir published [past tense] The Second Sex in 1949. In the book she contends [present tense] that woman....") If you're confused, think of it this way: History is about the past, so historians write in the past tense, unless they are discussing effects of the past that still exist and thus are in the present. When in doubt, use the past tense and stay consistent."

I would always use the past tense for primary sources. I would only ever use the present for current debates and writing in secondary sources.