Complex sentence: Such garments have been traditionally used at least from the 15th century in festivities such as Holy Week, symbolizing the act of penance, but these are totally unrelated to the KKK except by its superficial resemblance.
Split into simpler sentences: Such garments have been traditionally used at least from the 15th century in festivities such as Holy Week, symbolizing the act of penance. It is unrelated to the KKK except by its superficial resemblance.