SB 8.10.41

balir mahendraṁ daśabhis
 tribhir airāvataṁ śaraiḥ
caturbhiś caturo vāhān
 ekenāroham ārcchayat
Word for word: 
baliḥ — Mahārāja Bali; mahā-indram — the King of heaven; daśabhiḥ — with ten; tribhiḥ — with three; airāvatam — Airāvata, carrying Indra; śaraiḥ — by arrows; caturbhiḥ — by four arrows; caturaḥ — the four; vāhān — mounted soldiers; ekena — by one; āroham — the driver of the elephants; ārcchayat — attacked.
Translation: 
Mahārāja Bali then attacked Indra with ten arrows and attacked Airāvata, Indra’s carrier elephant, with three arrows. With four arrows he attacked the four horsemen guarding Airāvata’s legs, and with one arrow he attacked the driver of the elephant.
Purport: 

The word vāhān refers to the soldiers on horseback who protected the legs of the carrier elephants. According to the system of military arrangement, the legs of the elephant bearing the commander were also protected.