Grammar behind 言うには

Question

I recently came accross this sentence:

旅人が言うには、腹を空かせた野生の動物たちが、山を下りているらしい。

Which I understand roughly translates to "According to the travellers, some hungry animals came down from the mountain. What I do not understand is how 言うには works here. I could be wrong, but it doesn't seem to fit に + contrastive は.

I would like to know how には plays a part in the meaning "according to". Or maybe if 言うには is just a set phrase, I would be satisfied with that explanation as well.

Answer 1

This に is a particle explained here: What does the に do in 表情から察するに? This は is a topic marker and is optional here.

This type of に is literary and used mainly in written Japanese. It attaches to only a small group of verbs (言う, 見る, 聞く, 思う, 考える, 察する, etc.) in modern Japanese, so I think it's okay to think of them as just a group of similar set phrases. (In classical Japanese, it was a simple conjunctive particle similar to と.)