Śrīmad-Bhāgavatam · Text 3.11.19
Who is speaking and story frame
Speaking:Maitreya Ṛṣisince 3.11.18inside 3 frames: Sūta Gosvāmī → the sages at NaimiṣāraṇyaŚukadeva Gosvāmī → King ParīkṣitMaitreya Ṛṣi → Vidura
चत्वारि त्रीणि द्वै चैकं कृतादिषु यथाक्रमम् ।
संख्यातानि सहस्राणि द्विगुणानि शतानि च ॥ १९ ॥
catvāri trīṇi dve caikaṁ
kṛtādiṣu yathā-kramam
saṅkhyātāni sahasrāṇi
dvi-guṇāni śatāni ca
Translation
The duration of the Satya millennium equals 4,800 years of the years of the demigods; the duration of the Tretā millennium equals 3,600 years of the demigods; the duration of the Dvāpara millennium equals 2,400 years; and that of the Kali millennium is 1,200 years of the demigods.
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