"Beijing" means "northern capital," and "Nanjing" means "southern capital."
There is even a "Dongjing" or "eastern capital" that is WAY east of China. It's the city that the Japanese call "Tokyo."
Was there ever a "Xijing" or "western capital?" There is Chinese city called "Xi An" or "western peace" which may have been a capital of part of China at one time. Was this city, or any other city, Chinese or otherwise, ever referred to as "Xijing?" Put another way, did anyone ever name a western capital city Xijing just because of its relative importance to Beijing, Nangjing, and Dongjing?