Three forks braided into one great river system — the Green, the Blue, and the Red — that together water half the riverlands and have carried more marching armies than any road in Westeros. Kings have crossed it going both ways; not all of them made the return trip.
The Trident rises in the high ground of the Vale and the hills near the God's Eye and runs down through the riverlands in three separate courses before the Green Fork and Red Fork join the Blue near Riverrun, giving the Tullys both their seat and their sigil. Where the river runs shallow enough to ford, those crossings have decided the fate of kingdoms rather more often than the maesters would like to record.
It was at one such ford, in the last days of Robert's Rebellion, that a prince of dragon's blood met a stag-antlered lord in single combat over a woman neither of them lived to keep, and the rubies scattered from the prince's ruined armor are said even now to work loose from the riverbed after a hard rain — a claim the Citadel has never troubled itself to verify.
In the timeline
SourcesAGOT · EddardTWOIAF · The Riverlands
Where is The Trident?
Three forks braided into one great river system — the Green, the Blue, and the Red — that together water half the riverlands and have carried more marching armies than any road in Westeros. Kings have crossed it going both ways; not all of them made the return trip.
Is The Trident from the books or the show?
Book canon. This entry follows George R. R. Martin's novels and histories, and notes where the television series diverges rather than following it.