Travelers have been collecting souvenirs, little (or large) mementoes of places visited and events attended, for centuries. Historians point out that Alexander the Great sent caravans loaded with souvenirs from the Mediterranean countries he conquered. The Europeans visiting the Holy Lands even before the Crusades returned with reminders of their pilgrimages. Millions of vacationers purchased trinkets of their travels, or they collected for free seashells from the shores they walked or stones from the mountains they climbed. Even the crew of Apollo 11 grabbed moon rocks to commemorate their historic mission. As we travel, we search for the perfect reminder of a great vacation or an enjoyable country. Whatever trinket we chose to bring back, we prize them because they invoke in us feelings of nostalgia and memories of things we have enjoyed.