The Baths of Diocletian superimposed onto the modern-day area. Pen on paper.
Baths of Diocletian
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built: c.306ad
Diocletian is generally considered to have been one of the most effective administrators of the Roman Empire, he reformed it's legal and economic systems and created a power structure which divided the territories controlled by Rome into manageable portions. He is also known for his attempt to drive back the Christian wave that was engulfing the Empire, with a severe crackdown on the leaders of a movement which he saw as a mortal threat to political stability. A crackdown that simply fed the popularity of Christianity (Diocletian himself realized this and eventually repealed his edicts) by creating a pantheon of local and national martyrs who would be the figureheads of the religion once it was officially sanctioned by Constantine less than a decade later.