Fourth Age, year 1824. Date unknown.
The behemoths have never been a stable race, or particularly predictable. They may be useful, but their influences and actions have meant losing two years of digging through cave-ins and countless resources being spent on taming them, often with no luck. Our problems stem from them being near-impossible to kill or herd back through their portals should they become unruly. Once they are here, they are here permanently it seems. Runebinding is the elegant but expensive solution, whereby a behemoth is infused with rune magic and then controlled by magical pulses through a series of pillars. Lexicus came up with the system, before his mind wandered, and we haven't been able to improve on it since.