The Spine of Sirdanth is the name in the Heartlands for Avishraa's highest mountain range, which separates southern Sekhaa from the Brightness in the heart of the continent.

The range's name is a reference to a post-Imperial legend regarding the giantess Sirdanth, slain by the might of the semi-historical hero - and later empress - Chorreth, and the cunning of her frequent lover Kudath. Sirdanth was said to have been so immense that as her skeleton, rejected by Ba'uk, became buried in the earth, the spine was still visible as the mountain range.

As might be expected, such a prominent feature has different names among other languages and cultures. Many xtauh tribes of the far interior of the Brightness, to whom the mountains are rarely seen and near-legendary, know them as the Gray Highlands.

The Spine is, on average, the highest-altitude mountain range on Avishraa. Its highest point is the peak of Tiiren, in the north-central part of the range. It remains a debatable point whether Tiiren is the highest point on Avishraa, for the tallest peak of the mountains Enarri's northern coast is in the same range of altitude, though the range as a whole is much narrower and much lower than the Spine.

The Spine runs approximately northeast to southwest across the neck of land joining southern Sekhaa to the rest of the continent. Lying underneath the intertropical convergence zone of Avishraa's atmospheric circulation cells, prevailing winds bring moisture both from north and south; between both atmospheric convection and orographic lift, the air is forced to rise and and cool and release its moisture as precipitation. The slopes of the range have notoriously heavy precipitation on both sides, forming the basis for the large rivers that supply water to large stretches of the continent; the mighty Sahvarr River, the lifeblood of the Empire, flows from it, as do the rivers that bring corridors of green north across the Brightness before emptying into the distant Crimson Sea.

The Spine is not only a barrier to winds and weather. Though some of the lower reaches of the valleys nestled between the mountains are, up to a point, habitable to takmar, the region as a whole remains marginal territory for them due to their sensitivity to cold. Xtauh, whose environmental tolerances are somewhat more flexible, fare rather better, and in past ages were once the primary inhabitants of range and its surrounds, but the encroachment of takmar on the most habitable stretches has seen the xtauh tribes dwindle. Few mountain xtauh tribes remain, and most of those are in danger of extinction.

Despite its relatively inhospitability to takmar, the Spine has proven to be a haven for the Chosen. The discovery in the Steel Era of the hidden valley now known as the Citadel by a band of Chosen refugees provided a place where they could be isolated from their nonmagical kin - and where, inexplicably, other Chosen could, over the cycles, find their way. Protected from the south by the lower spurs of Tiiren and the volcano Vana Idrizal, and discouraging outside exploration from the north by sheer cliffs and violent weather in the upper Dhirim valley, takmakind at large has generally failed to become aware of the tiny civilization growing there.

The temperatures and weather in the Spine of Sirdanth make traveling over it by flying a suicidal prospect, nor are there many routes through it that takmar can readily survive. Aside from traveling around the mountains along the coasts, there are two passes commonly used. The less difficult one is Tavath's Gap, which runs approximately east-west between the Sea of Twilights and the Gulf of Shaad, through the western end of the range. The top of the pass is relatively low and the path more gradual than that of Barith's Gate, and it is by far the more casually used of the two; sea travel is less developed in this part of Sekhaa, and the pass provides the most direct route to southwestern Sekhaa, the valleys of the northwestern Spine, and the Sea of Grass.

The other pass, Barith's Gate, runs north-south through the eastern Spine. Higher, more rugged, and less climatically hospitable to takmar, it remains the most direct land route between the takma states of the southern Brightness and those of the Heartlands, but more dangerous than the narrow coastal route that parallels it, in a longer and more indirect way, along the Windward Sea. Because the ships of the Abethine Sea city-states are frequently seen on this side of the continent, many of those who can afford their services find it quickest and safest of all to avoid the land routes entirely and travel or ship goods by sea.