Matsyapurana 129.33

129.33

purāṇyekaprahāreṇa śatāni nihaniṣyati
āyasaṃ tu kṣititale rājataṃ tu nabhastale //

He said to himself — "I, alone, should live in that Tripura fort It ought to be built in such a way as no one amongst the Devas might be able to destroy it with a single arrow' He thought also "I should make each of the three fortresses 100 yojanas in length and breadth The building would be commenced and completed under the Yoga of the asterism Puṣyâ, when the above three cities would rise and meet the celestial firmament and whoever would get hold of and attack the above cities under this Puṣyâyoga would be able to destroy them by means of only one arrow shot by him The lowest fort, that on earth, is to be made of iron, the one in the celestial firmament is to be made of silver, and the topmost one is to be built of gold These three combined would be known as the 'Tripura' fort The length and breadth of this is to be one hundred yojanas each, and it will be impregnable to all It will be decorated with many palatial buildings various instruments, various weapons sataghnis chakras spears, upalas kampanas and various other arms Hundreds of towers and turrets would be built to make the cities look like the great Mandara and Meru Who can destroy, save the three eyed Bhagavan (Śiva), these three cities touching the Heavens, and so well guarded by myself, Târaka and Vidyunmālī? —29 36