Namhansanseong was a strategic military fortressprotecting Hanyang, and it is one of the most significant sites in the historyof Catholic persecution in Korea. From the Shin-haePersecution (1791) to the Gi-hae Persecution (1839) andthe Byung-in Persecution (1866),nearly 300 Catholics were executedhere by beheading, hanging, clubbing, and other brutal methods.

During the Byung-in Persecution, the torture knownas Baekjisa began. Victims were bound, water was poured overtheir faces, and layers of mulberry paper were pressed repeatedly against themuntil they suffocated. Within the fortress remain the former tribunal whereCatholics were interrogated, the execution ground, the military drill hallwhere believers were used as training objects, the ravine where the bodies ofmartyrs were discarded, and the execution site of BlessedThomas Han Deok-un outside the East Gate.