Vishnupurana 5.23.11

5.23.11

tasmād durgaṃ kariṣyāmi yadūnām aridurjayam
striyo 'pi yatra yudhyeyuḥ kiṃ punar vṛṣṇipuṃgavāḥ //

When Krishńa knew of his approach, he reflected that if the Yádavas encountered the Yavana, they would be so much weakened by the conflict, that they would then be overcome by the king of Magadhá; that their force was much reduced by the war with Magadhá, whilst that of Kálayavana was unbroken; and that the enemy might be therefore victorious. Thus the Yádavas were exposed to a double danger. He resolved therefore to construct a citadel for the Yadu tribe, that should not be easily taken; one that even women might defend, and in which therefore the heroes of the house of Vrishńi should be secure; one in which the male combatants of the Yádavas should dread no peril, though he himself should be drunk or careless, asleep or abroad. Thus reflecting, Krishńa solicited a space of twelve furlongs from the ocean, and there he built the city of Dwáraka, defended by high ramparts, and beautified with gardens and reservoirs of water, crowded with houses and buildings, and splendid as the capital of Indra, Amarávatí. Thither Janárddana conducted the inhabitants of Mathurá, and then awaited at that city the approach of Kálayavana.