The largest modern snakes top out at around 10 meters, probably closer to 9 (not that there's anything small about that). But a reptile whose remains were dug out of a Columbian coal mine could have swallowed the largest of its modern rivals for breakfast. Titanoboa cerrejonensis was about 13m long and weighted better than 1,100 kg. Some 60 million years ago at the end of the Cretaceous period, this was the top predator in its aquatic environment, constricting crocodilians and anything else that was handy.
Paleontologist Jason Head explained, "It's the biggest snake the world has ever known. The snake's body was so wide that if it were moving down the hall and decided to come into my office to eat me, it would literally have to squeeze through the door."
COMMENT: Wow. This does make one think about the modern reports of giant anacondas and boa constrictors (this snake was related to both) measuring 15m or more. However, the team Head was on estimated the tropics must have been considerably warmer than they are today to make a cold-blooded snake of this size practical from an energy standpoint. I can never resist quoting David Quammen's summary of monster snake lore: "It might all be true but it probably isn't."