Judaism is the oldest monotheistic religion in the world with over 3,000 years of history. Christianity and Islam also trace their roots back to Abraham. The pope had power over leaders and could excommunicate or deny salvation to those who disobeyed. Guilds were organizations of people in the same occupation such as bakers or glass makers. Charlemagne was a strong ruler who conquered a vast territory and encouraged Christianity and education. He was the first Holy Roman Emperor and is sometimes called the "Father of Europe".