Arthashastra
पर्वत अन्तर् द्वीपाश् च दुर्गा न अध्युष्यन्ते जन पद अभावात् ॥
When a country consists purely of cultivators, troubles due to the absence of fortifications (are apparent)
english translation
parvata antar dvIpAz ca durgA na adhyuSyante jana pada abhAvAt ॥
hk transliteration by Sanscript