They counted to 60 by counting the 3 phalanges on each finger on one hand and with their other hand they indicated each time they added 12 more numbers to their count. So by adding 12 numbers 5 times they were able to count to 60! This is base 60, also known as the sexagesimal number system.
3 * 5 * 4 = 60
Actually quite intuitive and impressive.