uses the term "political martyrs" for men of "high estate", including kings and bishops, who were killed during the Late Middle Ages during the course of the rebellions, civil wars, regime changes, and other political upheavals of the 14th and 15th centuries. Piroyansky notes that although these men were never formally canonized as saints, they were venerated as miracle-working martyrs and their tombs were turned into shrines following their violent and untimely deaths. J. C. Russell has written that the "cults of political saints" may have been a way of "showing resistance to the king" that would have been difficult to control or punish. Degrees of martyrdom Some Roman Catholic writers (such as Thomas Cahill) continue to use a system of degrees of martyrdom that was developed in early Christianity. Some of these degrees bestow the title of martyr on those who sacrifice large elements of their lives alongside those who sacrifice life itself. These degrees were mentioned by Pope Gregory I in Homilia in Evangelia; in it he wrote of "three modes of martyrdom, designated by the colors, red, blue (or green), and white". A believer was bestowed the title of red martyr due to either torture or violent death by religious persecution. The term "white martyrdom" was used by the Church Father Jerome, "for those such as desert hermits who aspired to the condition of martyrdom through strict asceticism". Blue (or green) martyrdom "involves the denial of desires, as through fasting and penitent labors without necessarily implying a journey or complete withdrawal from life". Also along these lines are the terms "wet martyr" (a person who has shed blood or been executed for the faith) and "dry martyr" (a person who "had suffered every indignity and cruelty" but not shed blood, nor suffered execution). Christian martyrs today The Center for the Study of Global Christianity of Gordon–Conwell Theological Seminary, an evangelical seminary based in Hamilton, Massachusetts, previously estimated that 100,000 Christians die annually for their faith, although the CSGC has now disavowed this estimate. Archbishop Silvano Maria Tomasi, permanent observer of the Holy See to the United Nations, later referred to this number in a radio address to the 23rd session of the Human Rights Council. The methodology used in arriving at the estimate of 100,000 has been widely criticized. The majority of the one million people the Center counted as Christians who died as martyrs between 2000