Behemoths came in many shapes and sizes though, as their name implied, the best known were typically very large. Behemoths could be either herbivorous or carnivorous, depending on the species. Unlike dragons, behemoths were incapable of speech and were non-intelligent by nature.
Behemoths came in many varieties, from small to large, but most shared a number of physical features. Behemoths were, for instance, all covered in a layer of pebble-like skin. Most also demonstrated a well-developed sense of smell, which predatory behemoths used to hunt.  Many were also herbivorous.
Like dragons, predatory behemoths had a powerful lust to hunt, their razor-sharp teeth suitable for rending prey apart and were also highly territorial. Herbivorous behemoths were usually less aggressive although when defending their young or wounded or after being startled or irritated, they could be vicious enemies 
It was widely believed by scholars from Candlekeep that behemoths existed in Toril since before the time period known as the Days of Thunder. In those ancients times, various species of behemoths thrived until a cataclysm changed the world so drastically that most of the behemoths went extinct.
Sages from Candlekeep didn't had a unified theory about the nature of the catastrophe. The most commonly accepted theory proclaimed this catastrophe was the Tearfall, while detractors of this theory believed that the sun temperatures diminished to a degree that produced a global climatic change so harsh that only the smallest behemoths were able to survive. A lunatic sage even proclaimed the cataclysm was actually a war between the gods and their enemies.
Behemoths often lived in areas very much isolated from humanoid habitation. They usually were found in remote mountain valleys, isolated rocky plateaus, dense tropical island forests, or secluded in the deepest and darkest of the jungles.
There were multiple species of behemoths, some of which are listed below.
A species of herbivorous behemoth with a duck like mouth, they are timid and easily frightened.
- Bloodspike behemoth
- Herbivorous behemoths marked by large plates resting along their spine and a notoriously bad temper.
- A large, carnivorous variety of behemoth marked by a horn-like ridge along its snout.
- Small, predatory behemoths roughly the size of humans that were highly social.
- An aquatic species of behemoth roughly fifty feet in length, much of which was from its extremely long neck and serpentine tail.
- Macetail behemoth
- Macetail behemoths were extremely territorial behemoths, covered in natural armor from head to toe.
- Superficially similar to deinonychus, though much larger, megaraptors were notable for their large hand claws.
- An enormous flying behemoth that fed on fish. They were common in Chult.
- Short-tempered and aggressive even for a herbivore, triceratops were recognizable by their three horns and armored head.
- Tyrannosaurus Rex
- Among the largest predatory behemoths, tyrannosaurus was both a predator and a scavenger.
- ↑ Wizards RPG Team (2014). Monster Manual 5th edition. (Wizards of the Coast), pp. 79–80. ISBN 978-0786965614.
- ↑ Skip Williams, Jonathan Tweet, Monte Cook (July 2003). Monster Manual 3.5. (Wizards of the Coast), p. 60. ISBN 0-7869-2893-X.
- ↑ Frank Mentzer (January 1985). “Ay pronunseeAYshun gyd”. In Kim Mohan ed. Dragon #93 (TSR, Inc.), p. 25.
- ↑ Ed Greenwood, Eric L. Boyd, Darrin Drader (July 2004). Serpent Kingdoms. (Wizards of the Coast), p. 148. ISBN 0-7869-3277-5.
- ↑ 5.0 5.1 5.2 5.3 Skip Williams, Jonathan Tweet and Monte Cook (October 2000). Monster Manual 3rd edition. (Wizards of the Coast), p. 55. ISBN 0-7869-1552-1.
- ↑ Mike Mearls, Stephen Schubert, James Wyatt (June 2008). Monster Manual 4th edition. (Wizards of the Coast), p. 31. ISBN 978-0-7869-4852-9.
- ↑ Brian R. James and Ed Greenwood (September, 2007). The Grand History of the Realms. (Wizards of the Coast), p. 8. ISBN 978-0-7869-4731-7.
- ↑ Nigel Findley, et al. (October 1990). Draconomicon. (TSR, Inc), p. 7. ISBN 0-8803-8876-5.
- ↑ 9.0 9.1 Nigel Findley, et al. (October 1990). Draconomicon. (TSR, Inc), p. 8. ISBN 0-8803-8876-5.
- ↑ Ed Greenwood, Eric L. Boyd, Darrin Drader (July 2004). Serpent Kingdoms. (Wizards of the Coast), p. 66. ISBN 0-7869-3277-5.