An Ice Core Reveals the Economic Health of the Roman Empire
nytimes.com
nytimes.com
[0] https://fallofromepodcast.wordpress.com/
[1] https://www.stitcher.com/podcast/wondery/tides-of-history
which has the graph and a little more information than the nytimes article
They are commonly grouped together as phases of classical antiquity.
Scientists create hypotheses on the basis of information available to them; if more information arrives, the hypotheses are (eventually) adjusted accordingly. They're not meant to be taken as absolute assertions.