Arthashastra
अतिदुर्ग प्रतिष्टब्धं वा सामन्त आटविक तत् कुलीन अपरुद्धानाम् अन्यतमेन अवग्राहयेत् ॥
If he has entrenched himself in an exceptionally inaccessible fortress, he should be besieged and captured by employing either a neighboring ruler, a forest chieftain, a member of his own family, or an exiled prince.
english translation
atidurga pratiSTabdhaM vA sAmanta ATavika tat kulIna aparuddhAnAm anyatamena avagrAhayet ॥
hk transliteration by Sanscript