When Alexander the Great invaded northwestern India, who was the ruler of Taxila that chose to ally with him?

Introduction / Context:
Alexander the Great's invasion of northwestern India in 326 BCE brought him into contact with various local rulers. Some resisted him, while others allied with him for strategic reasons. Taxila was an important political and cultural centre at that time, and knowing who ruled Taxila and what stance he took toward Alexander is a regular feature of ancient Indian history questions, especially because it contrasts with the resistance offered by other kings like Porus.

Given Data / Assumptions:

• The incident is Alexander's invasion of northwestern India around 326 BCE.
• The city in focus is Taxila, a major centre in the Punjab–Gandhara region.
• The options list Ambhi, Porus, Ashoka and Bimbisara as possible rulers.
• We assume students know that some Indian rulers cooperated with Alexander and others fought him.

Concept / Approach:
When Alexander approached Taxila, the ruler of the city, known in Greek sources as Omphis and in Indian sources as Ambhi, decided to ally with Alexander rather than resist him. He welcomed Alexander and helped him in his campaign against other local rulers, most famously Porus. Porus, by contrast, ruled the region between the Jhelum and Chenab rivers and fought against Alexander at the Battle of the Hydaspes. Ashoka and Bimbisara belong to different dynasties and time periods and are not associated with Taxila during Alexander's invasion. Therefore, the correct answer is Ambhi.

Step-by-Step Solution:
Step 1: Fix the time period: Alexander's Indian campaign took place around 326 BCE. Step 2: Identify Taxila as a wealthy and strategic city in the Gandhara–Punjab region. Step 3: Recall that the ruler of Taxila at that time was Ambhi, also called Omphis in Greek accounts. Step 4: Remember that Ambhi chose diplomacy and alliance, welcoming Alexander and gaining his support against rivals. Step 5: Distinguish Ambhi from Porus, who ruled a neighbouring region and fought Alexander at the Hydaspes. Step 6: Note that Ashoka and Bimbisara were Magadhan rulers from different centuries, not rulers of Taxila. Step 7: Conclude that Ambhi was the ruler of Taxila who allied with Alexander.

Verification / Alternative check:
Ancient Greek historians such as Arrian and Curtius mention a king named Omphis at Taxila, who submitted to Alexander and provided troops and supplies. Indian traditions identify this Omphis with Ambhi. Standard Indian history textbooks routinely state that Ambhi of Taxila allied with Alexander, while Porus opposed him. Ashoka belongs to the Mauryan dynasty roughly a century later, and Bimbisara ruled Magadha earlier in the 6th century BCE, confirming that neither matches the Taxila king during Alexander's invasion.

Why Other Options Are Wrong:

• Porus: He ruled the region of the Hydaspes (Jhelum) and is famous for fighting Alexander, not for ruling Taxila or allying with him.
• Ashoka: A Mauryan emperor who ruled long after Alexander and is associated with Magadha, not Taxila during the invasion.
• Bimbisara: A 6th century BCE ruler of Magadha, again unrelated to Taxila at the time of Alexander.

Common Pitfalls:
Many students confuse Ambhi and Porus because both appear in the context of Alexander's Indian campaigns. The key difference is that Ambhi allied with Alexander while Porus resisted him. Another pitfall is to forget the time gap between Magadhan rulers like Ashoka and Bimbisara and the period of Alexander. To avoid errors, memorise the simple pairing: Taxila and alliance with Alexander equals Ambhi, while heroic resistance at the Hydaspes equals Porus.

Final Answer:
When Alexander invaded India, Taxila was ruled by Ambhi, who chose to ally with him.