fl. 25 b.c.
In 25 b.c., Aelius Gallus led a military expedition to the region the Romans called "Arabia Felix," or modern-day Yemen. His mission was to extend Roman control throughout the Arabian Peninsula and gain for his emperor the wealthy spice-producing states at the peninsula's southern tip, but things did not turn out as planned. What he gained was not a new province, but a lesson for the seemingly invincible empire: that even Rome, with all its power and irresistible influence, had its limits.
The details of Aelius's life prior to his expedition are a mystery. He served as prefect of Egypt, a position in which he succeeded Gaius Cornelius Gallus (c. 70-26 b.c.), though his familial relation to that other Gallus—if any—is likewise unknown. In any case, soon after taking his post, Gallus received orders from Augustus (63 b.c.-a.d. 14), Rome's first emperor, to undertake an expedition to Arabia.
Roman knowledge of Arabia was sketchy at best. The Romans knew that trading caravans plied the peninsula, and that the southern kingdoms possessed great wealth, but as to what lay in between, they possessed only vague knowledge of a wide desert expanse. Departing from the city of Cleopatris on the Gulf of Suez, Gallus took with him a force composed of Egyptians, Jews, and Nabataeans, the latter an Arab people with whom the Romans had an uncertain alliance. The expedition got off to a bad start when their ships ran into trouble crossing the Gulf of Aqaba, and when they reached the city of Leuke Come or Haura on the Arabian Peninsula, an outbreak of sickness forced them to delay the expedition for half a year. Finally, however, they set out across the desert with a force of camels bearing water.
Traveling for some 80 days, the force conquered towns in the region of Negrana, or modern Nejran, then went on to a failed siege against Marsiaba or Marib in what is now Yemen. By then water supplies were running low, but Gallus's Arab guides insisted that they were only two days' march from the wealthy "incense states" of the coast. Two days eventually turned into six months, and finally Gallus retreated in disgust. His suspicions of his putative allies were confirmed when his return trip to the Red Sea took only 60 days instead of six months.
After reaching the sea, the army crossed to Myos Hormos, or Abu Scha'ar in Egypt. They had lost only seven men in actual battle, but their numbers had been greatly reduced by disease, hunger, and exposure—and not only had they failed to conquer Arabia, but they had gained little knowledge concerning the region. The principal intelligence gained from the Roman expedition, in fact, was much the same information gathered by the Soviets in their failed invasion of Afghanistan two millennia later: that some countries are so well protected by natural features and cultural barriers that the cost of conquest is simply too high for any imperial power.