Isaiah 21:7

‘Horsemen in pairs’ describes Arabs who were preparing to go into battle. The horsemen each rode an animal (camel or horse). But they each also led another animal (camel or horse). That is, each horseman took two animals. The second animal was to use for a quick escape, if the enemy won the battle. The *look-out needed to work out, even from a distance, who had won the battle. This is why the *look-out had to look so carefully.