Considered a mistake, the original design of the Stone Rhino was known as "Amaris' folly". Developed in a project whose objective was to create a BattleMech able to withstand an entire BattleMech company assault, these machines were to be launched into mass production and used to stop General Aleksandr Kerensky in his attempt to retake Terra. The prototype was described as a monstrosity whose leg actuators shut down during its first test run, so the project was summarily scrapped. However, the Word of Blake would use the engineering information for the Behemoth to create the first successful superheavy 'Mech, the Omega.
The Stone Rhino was one of the most remarkable surprises sprung upon the Inner Sphere by the invading Clans. Since the Inner Sphere forces knew about the Amaris Behemoth that was the name they gave to the 'Mech.
Bringing awesome firepower, these machines cannot be used effectively by commanders because they cannot afford to lose one. Mainly seen in Clan Smoke Jaguar, only a small number of these massive machines have been sighted. No other Clan appeared to field this design, but because it is a venerable design, other Clans are suspected to possess some, widely spread throughout their toumans. The Stone Rhino made use of eighteen tons of standard armor. It could jump up to ninety meters in one bound. [Source: sarna]
You can download the papercraft model here: Classic BattleTech - Stone Rhino (Behemoth) Free Mech Paper Model Download