The so-called Eighteen Heroic Passes had a more precise name within the Dou Ling Empire—Ten Perils and Eight Crossings.
The Ten Perils were a chain of death that the Dou Ling Empire had spent thousands of years painstakingly carving out and constructing along the precipitous, dragon-spine terrain of the Broken Spine Mountains, the last natural barrier before the great western river-valley plain.
These ten mighty passes resembled savage bone spurs on a dragon's back. Built around mountains, gorges, and narrow defiles, they were linked by hidden cliffside walkways, forming an enormous, three-dimensional defensive chain that extended hundreds of li in depth, with successive layers supporting one another.
Anyone attacking a single pass might simultaneously face reinforcements and firepower emerging from above, from the flanks, or even from within the mountains behind them.
The Eight Longitudinal and Transverse Lines, meanwhile, were eight behemoth-like fortress cities that the Dou Ling Empire had established at the confluences or strategic points of three great rivers—the Raging Waves, Clearwater, and Panlong—beyond the Ten Perils, on the relatively open but densely river-threaded great western river-valley plain.
Not only did these eight fortresses possess astonishing defenses of their own, but waterways extending in every direction also connected them into an enormous net covering the plain.
If any one city came under attack, the other seven could provide efficient, powerful mobile support by land and water within an extremely short time.
Although the Eighteen Heroic Passes had fewer garrison troops and smaller soul tool reserves than the Iron Triangle Fortress, their defensive resilience was far from ordinary, thanks to the naturally formed Ten Perils and the man-made network of the Eight Longitudinal and Transverse Lines.
According to the experience of the past several thousand years, even if the Heaven Dou Empire exhausted its strength to capture the Iron