The southern capital of the Panchala Mahajanapada was Kampilya.

Explanation:
Panchala was one of the Mahajanapadas, which were ancient kingdoms or republics in ancient India. The Mahajanapadas existed during the 6th century BCE to the 4th century BCE and were significant political and administrative units during that time.

The Panchala Mahajanapada was located in the northern part of present-day Uttar Pradesh, India. It had two main capitals - one in the north and one in the south. The northern capital was Ahichchhatra, while the southern capital was Kampilya.

- Panchala Mahajanapada:
Panchala Mahajanapada was situated on the banks of the river Ganges. It was divided into two parts - Uttara Panchala (Northern Panchala) and Dakshina Panchala (Southern Panchala). The kingdom was ruled by various dynasties, including the Bharata dynasty and the Kuru dynasty.

- Northern Capital - Ahichchhatra:
Ahichchhatra was the northern capital of Panchala Mahajanapada. It was an important city and a center of political power during ancient times. It is believed to be located in present-day Ramnagar in Uttar Pradesh. Ahichchhatra was known for its well-planned city layout and its administrative and economic significance.

- Southern Capital - Kampilya:
Kampilya was the southern capital of Panchala Mahajanapada. It was situated on the banks of the river Yamuna. Kampilya was an important city and played a crucial role in the political and cultural history of the region. It was known for its strategic location and its significance in trade and commerce.

- Importance of Kampilya:
Kampilya was strategically located at the confluence of the Yamuna and Ganges rivers. Its location made it an important center for trade and commerce. The city was also known for its cultural heritage and was home to various scholars and learned individuals. Kampilya was mentioned in ancient texts like the Ramayana and the Mahabharata, further highlighting its historical significance.

In conclusion, the southern capital of the Panchala Mahajanapada was Kampilya. It was an important city in ancient India, known for its strategic location, trade, and cultural significance.