The Apostle Paul spent roughly one-quarter of his missionary career in prisons. John McRay wrote in Christian History:
Roman imprisonment was preceded by being stripped naked and then flogged—a humiliating, painful, and bloody ordeal. The bleeding wounds went untreated as prisoners sat in painful leg or wrist chains. Mutilated, bloodstained clothing was not replaced, even in the cold of winter.
Most cells were dark, especially the inner cells of a prison, like the one Paul and Silas inhabited in Philippi. Unbearable cold, lack of water, cramped quarters, and sickening stench from few toilets made sleeping difficult and waking hours miserable. Because of the miserable conditions, many prisoners begged for a speedy death. Others simply committed suicide.
In settings like this, Paul wrote encouraging, even joyful, letters and continued to speak of Jesus.
