On the De Rerum Natura  "Nature of Things" by Titus Lucretius Carus, translated by William Eleary Leonard. The poems main purpose was to convey the Epicurian philosophical position and provide comfort for a Gaius Memmius. Ataraxia is described as a kind of peacefulness of mind  derived from suspending judgement, in terms of belief in the afterlife, the supernatural and political positions. The Stoics defined this as mental tranquility, apatheia, the absence of passion.

It has content that is a near the modern view,

     The narrow path of man's ambition;
     Since all their wisdom is from others' lips,
     And all they seek is known from what they've heard
     And less from what they've thought. Nor is this folly
     Greater to-day, nor greater soon to be,
     Than' twas of old.

There are things outside immediate human experience, that cannot be directly known within the human life span, it takes many generations of accreted knowledge. The limits of Titus Lucretius Caruses knowledge is thus, he knows the world is not eternal, uses a theory of atoms described by Democritus, he looks at mist and air and talks about ether. He describes a theory where the closer the planetary bodies and constellations are to the earth, the slower they move through the sky, thus the sun and moon move slower than star constellations. Looking at his descriptions of the origins of life, in Book V, he writes that "from the sky breathing creatures can never have dropped" and "Nor land dwellers have ever come up from the seas of salt" and thus what remains is that life came from the earth. This argument is justified by observation of the growth of plants, with the " concretion of rain and the heat of the sun" and he describes the earth by the metaphor of "Mother". In the absence of 2000 years of cultural evolution and the recent development of scientific enquiry I doubt I could reach a better conclusion. I find it interesting that he considers the other alternatives as well, this could be due to other sources, such as origin myths.

Near the end of book V it has a description of the plague of Athens, based on the description by Thucydides (431 BC) in his The History of the Peloponnesian War.

Its description via wikipedia is here.

 Various pathogenic sources have been suggested, including Measels (morbillivirus), Yersinia pestis, Salmonella typhi, influenza with a toxin producing staphylococci, more recently Rickettsia prowazekii and hemorrhagic viruses. The strongest argument seems to be for Rickettsia prowzekii, which is spread by the human body louse Pediculus humanus and is a small intracellar bacteria that stains poorly with Gram stain (Murray et al 2009 : 432). Clinical disease starts eight days after exposure with non specific symptoms, then myalgia, fever, headaches and potentially pneumonia, arthralgia and neurological involvement. A petechial or macular rash occurs in 20 to 80 % of patients. Mortality is around 20 to 30 % when untreated.

Ultimately the pathogenic source of the plague of Athens cannot be conclusively identified, there may be issues with Thucydides description.

Bibliography

Murray, Patrick : Rosenthal, Ken S & Pfaller, Michael A. (2009). Medical Microbiology. (Sixth Edition). Published by Mosby Elsevier. Page 432.