Final answer:
Alexander the Great's army reached its easternmost point at the Hyphasis River, today's Beas River, near the Indian Ocean. Retreating, they faced the challenging Makran Desert.
Step-by-step explanation:
The easternmost point to which Alexander the Great's army traveled was the Hyphasis River, which is known today as the Beas River, in the northern part of the Indian subcontinent. When Alexander's exhausted army refused to march further east, he agreed to turn back. The body of water near the easternmost point of Alexander's conquests is the Indian Ocean. After retreating, Alexander chose to follow the Indus River southward and ordered his army to split. The fleet went successfully by sea to the Persian Gulf, while the land forces suffered greatly crossing the Makran Desert, which bordered the Indian Ocean, leading to significant casualties.