The first invasion of Nubia
In 641 C.E. during the caliphate of Umar when 'Amr b Al 'Aas was the Governor of Egypt, an expedition under Uqba b Nafe' was undertaken against Nubia. The Nubians were very mobile, and as such no regular battle was fought. The operations consisted of skirmishes, haphazard engagements and hit-and-run raids. The Nubians were expert archers, and they caused considerable havoc among the ranks of the Muslims. Most of the Muslim soldiers lost their eyes. The war proved inconclusive, and the Muslim forces were Pulled out of Nubia without achieving any result.
Second invasion of Nubia
Ten years later, when Abdullah b Sa'ad was the governor, the Muslim forces invaded Nubia for the second time. The Muslim forces advanced into Nubia, and besieged Dongola the capital of Nubia. Here history repeated itself. The Nubian archers known as the "Archers of the Eye" let loose a shower of arrows aimed at the eyes of the Muslim warriors. The Nubians were expert marksmen, and their arrows caused a good deal of consternation among the Muslim ranks.
As the Muslims were not able to overpower the Nubians, they accepted the Nubian offer of peace. According to the treaty that was signed, each side agreed not to make any aggression against the other. Each side agreed to afford free passage to the other party through its territories. Nubia agreed to provide 360 slaves to Egypt every year, while Egypt agreed to supply grain to Nubia according to demand.