தெளிந்த நீர், வெட்ட வெளியான நிலம், உயர்ந்த மலை, அடர்ந்த காடு என்னும் இவையே நீர் அரண், நில அரண், மலை அரண், காட்டு அரண் என இயற்கை அரண்களாகும்.

ஆழமும் அகலமும் கொண்ட அகழ், பரந்த நிலம், உயர்ந்து நிற்கும் மலைத்தொடர், அடர்ந்திருக்கும் காடு ஆகியவற்றை உடையதே அரணாகும்

மணிபோல் தெளிந்த நீரும், வெட்ட வெளியான நிலமும், மலையும், அழகிய நிழல் உடைய காடும் ஆகிய இவை நான்கும் உள்ளதே அரண் ஆகும்.

A fort is that which has everlasting water, plains, mountains and cool shady forests

In Kural 742, Thiruvalluvar emphasizes the importance of natural resources and geographical features in determining the strength and resilience of a fort. He lists four key elements: clear water, fertile plains, high mountains, and dense forests. Clear water is vital for sustaining life. It is needed for drinking, farming, and other daily activities. Therefore, a fort situated near a source of clear water is beneficial for its inhabitants. Fertile plains symbolize agricultural productivity. A fort surrounded by such lands can support its population with enough food and other resources, thus ensuring their survival in times of siege or scarcity. Mountains serve as natural barracks, providing a strategic advantage. They act as a natural barrier against enemies, making a fort situated on or near a mountain harder to conquer. Dense forests offer cool shade and are a source of wood, fruits, and other resources. They can also serve as a natural camouflage, hiding the fort from enemy view. In essence, Thiruvalluvar suggests that a true fort is not just about walls and gates; it is about leveraging nature's bounty to ensure the fort's endurance and the well-being of its inhabitants. This verse is a testament to his deep understanding of geography, strategy, and sustainability.