If famine-inducing drought was indeed a factor, I'd say it was more likely the Romans simply decided to leave regardless. Why not fuck off at this point? A no-brainer? Why there has to be a 'heroic battle' steeped in history (code for BS generally) is a completely separate issue.
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https://youtu.be/PU0kQjr5eG8?si=paeVNqcjI5H-AiK7
for a drought