The Decapolis serves as a starting point for Aelius Gallus' ill-starred expedition in 25-24 BCE in search of Arabia Felix.

Aelius Gallus, the second praefect of Roman Egypt (Aegyptus) in the reign of Augustus during the years 26–24 BCE, had replaced Cornelius Gallus—with whom he has often been confounded.

Aelius Gallus is also known to be an intimate friend of the Greek geographer Strabo of Pontus and has been identified with the Aelius Gallus frequently quoted by Galen, whose remedies are stated to have been used with success in his Arabian expedition.

Gallus has undertaken the expedition from Egypt by the command of Augustus, partly with a view to explore the country and its inhabitants, and partly to conclude treaties of friendship with the people, or to subdue them if they should oppose the Romans, for it is believed at this time that Arabia is full of all kinds of treasures.

When Aelius Gallus sets out with his army, he trusts to the guidance of a Nabataean called Syllaeus, who deceives and misleads him.

A long account of this interesting expedition through the desert is given by Strabo—who derives most of his information about Arabia from his friend Aelius Gallus.

Strabo belongs on his mother's side to a famous family, whose members had held important offices under Mithridates V (around 150–120 BCE), as well as under Mithridates the Great (132–63 BCE), the opponent of Rome.

His first teacher had been the master of rhetoric Aristodemus, a former tutor of the sons of Pompey (106–48 BCE) in Nysa (now Sultanhisar in Turkey) on the Maeander.

Strabo in 44 BCE had emigrated to Rome to study with Tyrannion, the former tutor of Cicero, and with Xenarchus, both of whom were members of the Aristotelian school of philosophy.

Under the influence of Athenodorus, former tutor of Octavius, who probably introduced him into the future emperor's circle, he had turned toward Stoical philosophy, the precepts of which include the view that one unique principle ceaselessly pervading the whole universe causes all phenomena.

Before leaving Rome in 31 BCE, he had completed the forty-seven-volume Historical Sketches, of which but a few quotations survive.

A vast and eclectic compilation, it is meant as a continuation of Polybius' Histories.

The Historical Sketches covers the history of the known world from 145 BCE to 31 BCE—that is, from the Roman conquest of Greece to the Battle of Actium.

Strabo has traveled between Armenia and Sardinia and from the Black Sea to Ethiopia, incorporating both his own observations and earlier sources in his great work-in-progress, the Geography.

Strabo in 29 BCE had visited the island of Gyaros (today known as Yiáros, or Nisós) in the Aegean Sea, on his way to Corinth, Greece, where Augustus was staying.

Together with Aelius Gallus, he sails up the Nile in 25 or 24 as far as Philae.

The expedition to Arabia Felix, of which an account is given by his friend Strabo, as well as by Cassius Dio and Pliny the Elder, has turned out to be a complete failure.

The burning heat of the sun, the bad water, and the want of every thing necessary to support life, has produced a disease among the soldiers that is altogether unknown to the Romans, and destroys the greater part of the army; so that the Arabs are not only not subdued, but succeed in driving the Romans even from those parts of the country which they had possessed before.

Aelius Gallus has spent six months on his march into the country, on account of his treacherous guide, while he effects his retreat in sixty days, obliged to return to Alexandria, having lost the greater part of his force.

Aelius Gallus is recalled by Augustus for failure to pacify the Kushites and is succeeded as prefect by Gaius Petronius, a military genius and close friend of Augustus.