Angela Y. Davis, Are Prisons Obsolete? page 44

[T]he prison sentence, which is always computed in terms of time, is related to abstract quantification, evoking the rise of science and what is often referred to as the Age of Reason. We should keep in mind that this was precisely the historical period when the value of labor began to be calculated in terms of time and therefore compensated in another quantifiable way, by money. The computability of state punishment in terms of time--days, months, years--resonates with the role of labor-time as the basis for computing the value of capitalist commodities. Marxist theorists of punishment have noted that precisely the historical period during which the commodity form arose is the era during which penitentiary sentences emerged as the primary form of punishment.