There are so many history available for examination but the main thing is that we should use the ancient history and sources for better results for ever. That is not important how many times you have referred one thing but the important thing is that how you have refereed that thing. So it depends on the ancient history and its sources.
If it is not referenced, then yes, it constitutes as plagiarism. If it is referenced, then there should be no problem, provided the majority of your work isn't made up of quotes.
Ideally sources should be paraphrased, unless examining a specific aspect of the source where quotation is necessary to illustrate the argument. It is not plagiarism if the source is acknowledged.