The rocky backed thunderfoot is truly a sight to behold, standing over seventy feet in stature and over a hundred feet in length, one can easily mistake one for a walking building. With their immense weight of a hundred tons a marching herds sound like a thunderstorm.
Being creatures of such tremendous size, rocky backed thunderfoots have very little to fear apart from large predators. Because of their size they seldom even notice humanoids and adults usually just ignore them. Unsurprisingly considering with how they keep their heads held high and rarely ever glance down to the earth beneath them. However, when a rocky back is attacked, it never usually ends well for the attackers. With their surprisingly thick hides arrows rarely ever cut deep enough to inflict actual injuries to them.
Despite weighing more than a house made of stone, rocky backs can achieve a fairly imposing speed thanks to their stride, and unsurprisingly their legs can flatten almost anything caught underneath them. One account tells of a hill giant that made the mistake of picking a fight with one in the following:
I watched as the hill giant was angered the thunderfoot ate his share of food. He kicked it in the leg once, and then the massive beast stomped on the giant so hard his innards busted out. It was as morbid as it was hilarious.
Rarely do herds of rocky backs stay in place for more than a week. Constantly feeding on high growing conifers and palm leaves these behemoths eat constantly like all sauropods and are constantly migrating from various areas of vegetation to feed on. Allowing for areas that had been fed on to regrow for when they return. Since rocky backs use the same route every migration this can cause some problems when the environment in the path changes.
In a very humorous event a noblemen had built an arboretum in the path of a rock back's migration route. One Paulus the Elder was present for the event and wrote the following excerpt in one of his books:
I watched an entire herd of around thirty-six rocky back thunderfoots march straight through the noblemen's garden. The fifteen foot steel fence fold apart as if made out of wicker. The entire herd feasted upon all the conifers, cycads, and palm trees in a matter of minutes. And just continued marching as if everything was normal. The total damages were around three thousand gold pieces. I found it incredibly amusing, the noblemen...less so.
Of all siege beasts, the rocky back thunderfoot is among the most desired for groups of barbarians, orcs, and other wandering groups of nomads. While untamable as an adult, the hatchlings can be raised to handle saddles and understand commands. With their immense size they can easily support massive howdahs being built onto them. Housing vast groups of soldiers and weapons. Usually a lookout tower is even constructed on the top of the animals head able to support one medium sized humanoid.
Druid circles will even sometimes make huts upon the animals backs. Using the thunderfoots back spines as foundations for a shelter made usually of lightweight plant material. The rocky backs usually do not seem to mind the druid groups and have even been known to adjust their sleeping habits to allow for these shelters to remain up.
While many beasts can be connected to an elemental plane, rocky backs are particularly connected to the quasi-elemental plane of lightning. These beasts are almost always found on their own and usually most active during stormy weather, although some theorize that they actually are the cause of thunderstorms, and can usually be identified by a low blue glow their necks emit. While dragons lightning breathes come naturally a rock back must be "charged" so to say by being struck by lightning, which they seem to be able to summon when they rear up onto their back legs and let out a loud bellowing call.
To many people the sight is astounding, watching a beast as tall as a watchtower be struck by lightning and then channel it through their mighty throats, which can be identified by it glowing bright blue, and then letting it out in a blast as powerful as an adult blue dragon's.