Holmes has been Victorian, 50s, and contemporary. No reason he can't be middle-ages too.
Cadfael! Just Holmes hiding out in the past, after an experiment with a time machine sent him and Moriarty careening through time and space, jumping from life to life, striving to put right what once went wrong, and hoping each time that his next leap will be the leap home…
So, now we have Robin Hood, Sherlock Holmes and Quantum Leap tied together...