Dreaming of Times Gone By

A sleeping character dreams a vision of events past—sometimes long past—and certainly ones he never saw.

While they can be hard to fathom, like Dreaming of Things to Come, they are unable to be warded or fought off, since they are long gone. And unlike Dream Spying, the characters are seldom detected by the people they watch. Dream Weavers can send them. When a character is Talking in Your Dreams, the other can show them.

Usually used to reveal information. They are always, of course, true.

Beware, though, that sometimes the past is not an era friendly to human sanity.

Might be explained by the dreaming characters having lived in the past, or having an ancestor living in that past, in which case there are definite limitations to what he will dream of.

See Bad Dreams for dreams of the character's past and Exposition of Immortality for when the character actually lived through the past they're dreaming about.

Examples of Dreaming of Times Gone By include:

Anime and Manga

In AIR, Misuzu dreams of the time of Kannabi-no-Mikoto which was her "full-self". As the dream becomes more vivid, her body deteriorates because no human body can contain the entirety of Kanna's soul, eventually leading to her tragic death.
In Puella Magi Madoka Magica, Madoka dreams of things that have happened in the previous iteration of the Groundhog Day Loop.
In Cardcaptor Sakura, the eponymous character dreams of the time of death not of Clow Reed.
Happens several time to different characters in Shaman King.
A different take happens between Koyuki and Snow in MAR, they are essentially the counterparts of the same person, and so they share dreams of what's happening between their worlds. Given that both girls love him, this level of interaction helps to solidify them as his 'One True Love', yes, both of them.
- Snow dreams of Koyuki's memories of her and Ginta's past.
- Koyuki dreams of Snow's interactions with Ginta, and relates them to his worried mother to confirm to her that her son is alright, though in another world.
An old man's astral form entered Ranma's, from Ranma ½, dream showing him a date that had happened when the man was young.

Literature

In Andre Norton's Opal-Eyed Fan, the heroine dreams of a centuries ago Human Sacrifice on the island where she was shipwrecked.
- In Horn Crown the hero dreams of himself at a long-ago banquet -- where a woman talks with him and realizes he's from the future and gives him some aid.
In Robert E. Howard's Conan the Barbarian story "Shadows in The Moonlight", Olivia dreams of how the strange statutes had been men, Taken for Granite by a Physical God after they had tortured his son to death.
- This is a frequent trope in many of Howard's stories.
In JRR Tolkien's The Lord of the Rings, Frodo dreams of Gandalf's capture and escape from Isengard during Fellowship Of The Ring. Gandalf observed "Then it was late in coming". (Worth noting since he also has prophetic dreams.)
- Faramir tells Eowyn he often dreams of the fall of Numenor.
In Terry Pratchett and Neil Gaiman's Good Omens, Witchfinder Shadwell has a dream about seventeenth-century witch and prophet Agnes Nutter. Because of her prophetic ability, he is detected by her, leading to a Brick Joke; in the first account the book gives of her burning at the stake, it says that her last act was to look up at the sky and say "That goes for you as well, you daft old fool," and it's implied that she's talking to God. When Shadwell dreams about it, it becomes clear that she was actually saying it to him.
Several characters in H.P. Lovecraft stories are unfortunate enough to dream of the times when Gods and their servants walked the Earth. Those dreams are usually harmful to mind, body, sanity, or all three.
In Barbara Hambly's Bride Of The Rat God, a character dreams of the ancient ritual in which the cursed necklace was used.
In Stephen Hunt's The Rise of the Iron Moon, Purity's dreams are identified as telling of the long-distant past.
In Rick Riordan's The Throne of Fire, Sadie dreams of Ra's being forced from his position.
In Margaret Ball's No Earthly Sunne, Ellen dreams of Elizabethean times.
In Septimus Heap, Silas and Sarah Heap dream of Nicko and Snorri as the latter are walking across a snow-covered forest ... 500 years before.

Video Games

In the Girls Love Visual Novel Akai Ito, Kei dreams of the time of the Mizuki Tribe and their coalition with the human exorcists from the Capitol in their quest to vanquish Nushi. She also dreams of the fall of the Mizuki at the hands of their human ex-allies, and the subsequent suffering of Sakuya.
- Its sort-of sequel, Aoi Shiro, Syouko dreams of the time of Yasuhime and her exile to the southern islands to seal the <<Sword>>. This is Justified by having the blood of Yasuhime literally flowing in her veins -- she was brought back to life by Yasuhime, once.
This is the majority of the gameplay in Assassin's Creed games.
Happens to Aya Brea in Parasite Eve 2. It's not so much sleeping as it's fainting from exhaustion.
A major plot point in Final Fantasy VIII, and several gameplay sequences, are devoted to the main characters dreaming of past events involving Laguna Loire and his friends. This later turns out to be because of another character's magical power.
In Xenogears, Fei and Elly experience visions of themselves in the distant past. It's not until near the end of the game that the reason for these visions is revealed.
In Forevers End, Epoch regularly dreams of the past of the Crusades.
Zig-Zagged in the first Knights of the Old Republic. The Player Character and Bastila are having dreams that retrace the steps of Darth Revan and Darth Malak as they sought out the Star Maps. It's played off as Force visions until The Reveal at the game's three-quarter mark.

Web Comics

Pibgorn is sent back in time by the ghost, into a dream.
- Much later Dru's attempt to enter her dream finds her in a memory.
In Strays, Meela has one of a murder, and more after.
In Homestuck, an important Troll historical figure known as the Signless had dreams of life before he Scratched his universe, causing everyone's lives to be reset, inspiring him to spread anti-caste-system messages.

Web Original

In The Questport Chronicles, Mei has dreams of events long past, including an Eldritch Abomination's imprisonment and her mother's death.

Western Animation

Parodied in the South Park episode "I'm a Little Bit Country", in which Cartman tries to invoke this trope to get out of studying for an American history report.