Explanation: Gaius Aelius Gallus was a commander under the first Roman Emperor, Augustus. Gallus was ordered to undertake an expedition to conquer Arabia with 10,000 troops, including local allies - a relatively small army. If successful, it would have massively increased the tax revenues of Rome, as the Arabian states controlled the flow of spices and silk and other exotic imports from the east.

Despite considerable military success in open battle against the Arabian polities, the Romans were chipped away at by the unrelenting desert itself - stretched supply lines, unfamiliar environs, heat, exhaustion, and sickness took their toll. Eventually, Gallus withdrew from the region, making a two-month retreat from modern-day Yemen back to Roman-controlled Egypt, having lost a majority of the expeditionary force in the process - many of them during the retreat itself.