In the Year of the Consulship of Augustus and Taurus (26 BC/728 AUC) Aelius Gallus (Second Praefect of Aegyptus) was sent on an expedition to Arabia Felix. The expedition would experience some early treachery and then grow into a campaign to add a new and strategic province to the new Roman Empire.
Year of the Consulship of Augustus and Taurus (26 BC/728 AUC): Aelius Gallus lands his forces in Arabia Felix. After some early disasters such as lack of water and supplies it is discovered that Syllaeus, a Nabataean guide, has betrayed the expedition. After some reorganization and aid from allies in the Kingdom of Aksum, the expedition continues. The Himyarite Kingdom caused some problems for the expedition and then refused Roman 'friendship.' By the end of the year the Himyarites fell to Roman might.
Year of the Consulship of Augustus and Silanus (25 BC/729 AUC): Reinforcements arrive from Aegyptus. It is decided to conquer all of Arabia Felix and turn it into a new province for the empire. Aelius Gallus continues pushing his armies to the east. In this year Qataban and Saba fall to Roman forces.
Year of the Consulship of Augustus and Flaccus (24 BC/730 AUC): The Roman forces spend a large portion of this year consolidating their gains and setting the early basis for the province government in Aden. This pause in conquest gives their next opponent more time to prepare.
Year of the Consulship of Augustus and Varro (23 BC/731 AUC): The invasion of Hadhramaut begins. They put up a strong resistance against the Roman forces and their Aksum auxiliaries. A land and naval attack on the city of Qana eventually succeeds but fighting continues.
Year of the Consulship of Marcellus and Arruntius (22 BC/732 AUC): The remainder of Hadramaut is conquered. It takes several months to destroy the last scattered resistance.
Year of the Consulship of Lollius and Lepidus (21 BC/733 AUC): Parthian forces aid the inhabitants of he eastern portion of the peninsula, what is now being called Arabia Ulterior (Oman in the OTL). Fighting starts out fierce. An additional Legion is sent to reinforce the Roman expedition.
Year of the Consulship of Appuleius and Nerva (20 BC/734 AUC): As the Parthian Empire continues to harass Roman forces in Arabia additional legions are deployed along the existing border between the two empires. The Parthians back down with the treat of a large-scale war and the remainder of the desired territory is annexed into the new province of Arabia Felix.
The location of stronger Roman land and naval forces in Arabia allow them to enhance their existing trade routes with India and regions beyond. It also gives them a great flanking position against the Parthian Empire, a gladius at the soft underbelly of their rival.
I've wanted to create the divergence point for my Rome survives timeline for awhile. I got some inspiration from an article in Vol. VII, Issue 5 of Ancient Warfare. The article was "Legionaries in the Sea of Hercules" by J. Albert Morales. The reference to the disastrous expedition in 26 BC as well as the future importance of the region, especially in regards to trade with kingdoms in India, made the idea of a successful conquest and development of Arabia Felix appealing.
I'm planning on moving forward from this point to flesh out an outline of the rest of the history of the First Roman Empire. I'm using the Year of the Consulship of... dates since they were used instead of the AUC dates (I do plan to have the Second Roman Republic officially adopt the AUC system because the Consulship year reckoning can be a pain. However it can be useful in reminding me that the Consulship will change as the timeline changes).
Any suggestions or comments would be appreciated as I move things forward. I now have the bookends of this timeline - a successful campaign in Arabia on one end and a catastrophic nuclear war with Zhōngguó in 2766 AUC. Now I get to fill in the gaps :).
Wikipedia: Aelius Gallus, Himyarite Kingdom