Kautilya's Arthashastra 2.3.3

2.3.3

janapadamadhye samudayasthānaṃ sthānīyaṃ niveśayet, vāstukapraśaste deśe nadīsaṅgame hradasyāviśoṣasyāṅke sarasas taṭākasya vā, vṛttaṃ dīrghaṃ caturaśraṃ vā vāstuvaśena vā pradakṣiṇodakaṃ paṇyapuṭabhedanam aṃsapathavāripathābhyām upetam //

Or with ready preparations for flight the king may have his fortified capital (stháníya) as the seat of his sovereignty (samudayásthánam) in the centre of his kingdom: in a locality naturally best fitted for the purpose, such as the bank of the confluence of rivers, a deep pool of perennial water, or of a lake or tank, a fort, circular, rectangular, or square in form, surrounded with an artificial canal of water, and connected with both land and water paths (may be constructed).