Poul did a throwaway story that I’d love to see expanded into a series.
A group of time travelers from 4,000 AD travel back to Renaissance Italy. They run into an evil baron and his henchmen, including one very learned monk. A little torture and the Italians have their own time machine. They set up a base in 10,000 BC and raid across time. They know that the Time Patrol can only use things in the historical record, so as long as they keep a low profile they’ll never get caught.
I’d put ‘The Expanse’ at the head of the line