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Hearth-Under-Stone’s size grew exponentially in this period, requiring a redoubling of mining efforts into the mountain range, expanding living and working spaces as well as bringing up ores and precious stones. As the depths increased, the noise of pick and powder charge summoned the insectoids. This both required and allowed for a new set of heavy, full body armor. This armor would also help bring the fight to enemy forces too intelligent to charge into the booby trapped false entrance of the fortress-city.

The base ichcahupilli remains the same, due its extreme cost effectiveness. Manufacturing volume was so great that every adult of H.U.S could be expected to have one in good repair at any given time to the point where it became daily wear for large numbers of the populace.

The base plate helm would be built up with combinations of a chainmail coif and/or a bevor. Due to the size and ferocity of the insectoids and the volume of fire a sieging raid could produce , the narrowing of vision was a happy trade for a higher likelihood of retaining sight and facial features.

A full steel chest plate, in addition to gauntlets, greaves, and arm protection, was more reasonable within the temperature controlled and Sun-shielded city of Hearth-Under-Stone. While some regions could support animal-drawn carriages to help with the additional weight and discomfort, its overwhelming use case was in defensive battles in the home range rather than afar raids.

The billhook became the standard main armament for the city's defense force, evolving from the traditional spear. The point allowed it to act as a standard spear, keeping the cautious at bay while able to easily poke into softer targets. The hook allowed for grabbing onto shields, armor, or clothing to break ranks and open defenses and could curve around limbs and cut at joints. The spike allowed overhead strikes to focus into a single armor-punch point.