In Greek mythology, Hercules found it necessary to cross the Atlas mountains. But instead of crossing, he decided to use his superhuman strength and split the mountains in half. This connected the Atlantic Ocean to the Mediterranean Sea, creating the Strait of Gibraltar. What is left of the mountains on either side are known as the Pillars of Hercules. On the northern side is the Rock of Gibraltar and on the southern side is north Africa (there is some controversy as to which peak is the southern pillar.) The ancients believed that nothing lay beyond the pillars of Hercules, it was the end of the known world and the entrance to Hades.
Interestingly, there is a theory that the $ dollar symbol comes from the Pillars of Hercules. In the years after the discovery of the Americas, the king of Spain used the Pillars of Hercules as the coat of arms of Spain. The symbol was also put on the Spanish coins. The coins were called the Pillar Dollar in the British colonies of North America. The curvy scroll which wraps around the two pillars eventually become the S with two lines through it. There are several other theories about the origin of the $ symbol. But from now on, whenever I write it, I will remember standing on one of the Pillars of Hercules!