Bhagavatapurana 10.41.19

10.41.19

athāparāhne bhagavān kṛṣṇaḥ saṅkarṣaṇānvitaḥ /
mathurāṃ prāviśad gopair didṛkṣuḥ parivāritaḥ //

19. At a late hour on the following day the Almighty Lord Krishna, accompanied by Sankarshana and the gopas, entered Mathura with the purpose of sight-seeing in the city. 20. The Lord saw the city. It was provided with a high towered entrance built of crystals (diamonds), with huge golden doors and portals, with granaries and apartments of copper and brass, inaccessible through deep moats, and adorned with parks and beautiful gardens on the outskirts.