I think it shows what the human mind is capable of. Euclid wrote much of the Elements employing only a compass and a straightedge. And also if you consider that in ancient times, many mathematicians also combined their studies of mathematics with other professions or studies such as philosophy (Decartes), law (Viete), or poetry (Khayyam), it's truly amazing how they were able to do so much at a time when even books were hard to come by.