If you are going to set fire to the enemy’s castle or camp, you need to prearrange the ignition time with your allies.
—Yoshimori Hyakushu #83
When shinobi were on a mission, particularly at night, one of their most crucial and complex duties was keeping track of time. If this task seems simple, remember that shinobi did not have watches or clocks. They didn’t even have sand hourglasses until the early 1600s.1 To send and receive signals at the proper time, coordinate attacks, know when the enemy would be vulnerable, and more, shinobi had to develop methods to tell time reliably.
Historically, one way to mark the hours involved lighting ...