Foucault is famous for his work on power and the body. In Discipline and Punish, he addresses the penal system and how it has changed over time with the influence of power. At the beginning of "The Body of the Condemned," Foucault discusses the role of sovereign or absolute power, wielded by a select few over everyone else. During this period punishment was of the worst imaginable degree and all punishment was carried out publicly in a ritualistic and habitual manner: torture was common. It was important for absolutist power to be exercised via physical degradation of the body. In the United States, public executions have remained fairly humane compared to the gruesome torture methods of the feudal ages. Foucault frequently mentions Pennsylvania throughout "The Body of the Condemned," referencing Pennsylvania's progressive use of prisoners as laborers for public works. Foucault later goes on to explain how executions became "an additional shame" compiled atop the shame of trial and being condemned (Foucault, 1995, p.10).
Pennsylvania was the first state to ban public execution. However, Pennsylvanians were also the most execution-hungry state in the early United States. While Foucault mentions the state on a couple of occasions, he does not acknowledge their shift in penal systems as the result of humanitarian efforts. Instead, he believes their shift in punishments was from a shift of power. While public executions no longer existed and the sovereign power didn't need to explicitly inflict physical punishment on the body, a new power arose: disciplinary power. Under this new system, "in order to deprive the individual of a liberty that is regarded both as a right and as property," the body would need to be caught in a "system of constraints and privations, obligations and prohibitions" (Foucault, 1995, p.11).
As alternate forms of punishment emerged, Foucault referenced the Panopticon in his explanation of discipline. Disciplinary power was exercised as surveillance. In the example of the Panopticon, the guards are constantly watching the inmates from the center of the Panopticon and prisoners never know if they're being watched but they always assume so which forces them to think and act properly. This was a much more elaborate control of the body. Foucault also argued that knowledge was a key source of this power as power in and of itself is knowledge in all facets.
Foucault, Michel. “The Body of the Condemned.” Essay. In Discipline and Punish: The Birth of the Prison, edited by Alan Sheridan, 1–31. New York, New York: Vintage Books, 1995.
Foucault, Michel. “The Panopticism.” Essay. In Discipline and Punish: The Birth of the Prison, edited by Alan Sheridan, 195–225. New York, New York: Vintage Books, 1995.