The Lithuanian language is considered to be very conservative for its close connection to Indo-European roots. It is believed to have differentiated from the Latvian language, the most closely related existing language, around the 7th century. Traditional Lithuanian pagan customs and mythology, with many archaic elements, were long preserved. Rulers' bodies were cremated up until the conversion to Christianity: the descriptions of the cremation ceremonies of the grand dukes Algirdas and Kęstutis have survived.