राजधर्मप्रश्नः — Yudhiṣṭhira’s Inquiry into Rājadharma (Śānti-parva 56)
दुर्गेषु च महाराज षट्सु ये शास्त्रनिश्चिता: । सर्वदुर्गेषु मन्यन्ते नरदुर्ग सुदुस्तरम्,महाराज! मरु (जलरहित भूमि), जल, पृथ्वी, वन, पर्वत और मनुष्य--इन छः प्रकारके दुर्गोंमें मानवदुर्ग ही प्रधान है। शास्त्रोंके सिद्धान्तको जाननेवाले विद्वान् उक्त सभी दुर्गोमें मानव दुर्गको ही अत्यन्त दुर्लघ्य मानते हैं
durgeṣu ca mahārāja ṣaṭsu ye śāstra-niścitāḥ | sarva-durgeṣu manyante nara-durgaṃ sudustaram ||
Bhishma said: “O great king, those who are firmly grounded in the conclusions of the śāstras speak of six kinds of fortresses. Among all fortresses, they regard the ‘human fortress’—the defense constituted by men—as the most difficult to overcome.”
भीष्म उवाच
Effective defense and security ultimately depend most on people—trained, loyal, and organized human resources—more than on terrain or physical fortifications; hence the ‘human fortress’ is deemed the most formidable.
In the Śānti Parva’s instruction on kingship, Bhīṣma advises the king on principles of governance and protection of the realm, citing śāstric classifications of fortresses and emphasizing the superiority of manpower-based defense.