Although most Palossand today are small pokemon – perhaps large for a sandcastle, but only the height of a child – the more one eats, the more it can grow. A fully grown Palossand is every bit as sturdy a wall as the castles it resembles, if not moreso, for the sands of a desert berm (whether natural, artificial, or a pokemon) adapted to technological changes that rendered castles of wood or stone obsolete.
Alola has many pokemon adept at defense; the name "Toxapex" makes trainers understandably shudder from Kanto to Alola. But wars were not won solely by being last to faint; they were fought over protecting territory, and every aspiring Kahuna in Alola grasped the value of Palossand to shore up gaps in (or even to outright replace) the walls of villages, cities, or even, as realms grew larger, whole islands. These Palossand were too large to be easily defeated, while the holes in their towers (or their mouths, for that matter) were more than large enough to allow defenders the use of ranged weapons and pokemon attacks; as weapons grew stronger, Palossand too changed shape, growing lower and wider until they looked more like a trench than a tower.
The Palossand of Melemele and Akala were slain by Ula'ula's Kahunas in their attempts to unify the region. The Palossand of Ula'ula survives, the last remnant of this ancient and ever-important tactic of Alolan warfare – but generally, only Ula'ulas most nationalistic citizens remember that it is a pokemon at all. Haina still attracts visitors, who marvel at its diverse life, shifting sands, and weather found nowhere else in Alola; most mapmakers, unaware of its history, append to it the descriptor of "desert", just as most tourists make no note of the lack of either native scavengers or pokemon bones.