Pliny the Elder (AD 23-79) did not write the first encyclopedia in the world, but his encyclopedia, usually referred to in English as the Natural History, is the earliest one which survives in more than just fragments, and, as I say, Pliny was exceptionally fond of Elephants.
Pliny's Natural History consists of 37 books (Think books of the Bible -- a book was a unit of writing that would fit onto an average-sized scroll -- and not, for example, the much larger volumes of the Encyclopedia Britannica.) His descriptions of elephants cover the first several pages of book 8. He said that of all the animals, the elephant was closest to humans in intelligence. I do not know whether Pliny originated the belief that elephants never forget, but he did say that their memory was exceptional. He also said that when it came to honesty, wisdom, judgment, respect for the stars and reverence for the sun and moon, they actually very often out-did humans. (Pliny had a lot of reverence for the sun and moon.) He said that they are very gentle; for example, Pliny said, if an elephant happens to get caught in the middle of a herd of sheep, it would pick sheep up with its trunk to make sure that it would not step on them.
Pliny said that sometimes, elephants fell in love with humans. He said that they would gather up bunches of plants and drop them into the beloved human's lap. He said that when the beloved human was absent, the elephant would lose its appetite. He said that elephants in love were awkward and adorable.
He praised their courage, their loyalty to each other and also to humans, and their ability to be trained. He said that once, an elephant which was below-average in intelligence, and had repeatedly failed to perform a certain exercise correctly during military training, was discovered in the middle of the night, wide awake and practicing the exercise it was having so much trouble with.
He said that when baby elephants got tired, adult elephants carried them on their backs.
I don't know whether the idea that elephants are terrified of mice originates with Pliny, but he did say that elephants despise mice, and that if they see a mouse in the feed they will refuse to eat anything from that entire portion.
And Pliny has much more to say about elephants, much of it things which we today would tend not believe.
And the reason I'm telling you this is that until I reached book 8, I often found Pliny's writing style a bit boring (although sometimes information transmitted in that writing style was fascinating), but at the beginning of book 8, when it became obvious that Pliny was in love with elephants, I found it awkward and adorable, and well worth reading and recommending to other readers for what it says about Pliny, and not necessarily for insights about elephants unavailable elsewhere to the modern person.