Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 49
Sanskrit:
इति सम्मन्त्र्य भगवान् दुर्गं द्वादशयोजनम् ।अन्त:समुद्रे नगरं कृत्स्नाद्भुतमचीकरत् ॥ ४९ ॥
ITRANS:
iti sammantrya bhagavāndurgaṁ dvādaśa-yojanamantaḥ-samudre nagaraṁkṛtsnādbhutam acīkarat
Translation:
After thus discussing the matter with Balarāma, the Supreme Personality of Godhead had a fortress twelve yojanas in circumference built within the sea. Inside that fort He had a city built containing all kinds of wonderful things.