How did Protestant and Catholic numerologists use 666 against religious opponents?

Protestant and Catholic numerologists historically utilized the number 666 as a polemical tool to identify their religious opponents as the "Beast" of the Book of Revelation. This practice relied on gematria or similar systems of assigning numerical values to letters to derive specific names or titles from the number.123

• Protestant usage: In 1612, the Protestant theologian Andreas Helwig calculated the value of the Latin phrase Vicarius Filii Dei ("Vicar of the Son of God") by summing the Roman numerals contained within it. By omitting non-numeral letters, he arrived at 666, which he used to argue that the pope and the Roman Catholic Church represented the beast. Similarly, the Protestant theologian Michael Stifel identified Pope Leo X as the beast using these methods.12
• Catholic usage: In the 16th century, the Catholic numerologist Peter Bungus employed a similar approach to target the Protestant Reformation. By adding an "a" to the end of the name Martin Luther, Bungus was able to manipulate the calculation to equate the German reformer with 666.12

These exercises demonstrate how numerical symbolism was weaponized to delegitimize theological rivals by associating them with apocalyptic evil.14