qnli question: The ancient buddhist site  in the lower Krsna Valley can be traced to at least what century BCE? sentence: " They note that the ancient Buddhist sites in the lower Kṛṣṇa Valley, including Amaravati, Nāgārjunakoṇḍā and Jaggayyapeṭa "can be traced to at least the third century BCE, if not earlier."