And, perusing Adam Clarke's commentary on Daniel, I find this:
Daniel 10:13
But the prince of the kingdom of Persia withstood me - I think it would go far to make a legend or a precarious tale of this important place to endeavor to maintain that either a good or evil Angel Is intended here. Cyrus alone was the prince of Persia, and God had destined him to be the deliverer of his people; but there were some matters, of which we are not informed, that caused him to hesitate for some time. Fearing, probably, the greatness of the work, and not being fully satisfied of his ability to execute it, he therefore for a time resisted the secret inspirations which God had sent him. The opposition might be in reference to the building of the temple.