Śrīmad-Bhāgavatam · Text 12.2.39
Who is speaking and story frame
कृतं त्रेता द्वापरं च कलिश्चेति चतुर्युगम् ।
अनेन क्रमयोगेन भुवि प्राणिषु वर्तते ॥ ३९ ॥
kṛtaṁ tretā dvāparaṁ ca
kaliś ceti catur-yugam
anena krama-yogena
bhuvi prāṇiṣu vartate
The cycle of four ages — Satya, Tretā, Dvāpara and Kali — continues perpetually among living beings on this earth, repeating the same general sequence of events.
Read this verse on Vedabase.ioThis verse has no purport; its meaning is explained by the verses around it.
From Canto 10, chapter 14 onward, the translation and purports were completed by Śrīla Prabhupāda's disciples after his departure, and published by the Bhaktivedanta Book Trust.