Not least among those advances were two 13th-century inventions: ships that could cross oceans, and guns that could shoot the people the sailors met on the other side.

这些推动进步的发明中，特别要强调的就是13世纪发明的枪械和船舰。船舰使人类得以出海远航，枪械得以使人类在远航时遇到世界另一边的船员时可以拼杀。