Here, on Patan's Durbar Square, stands the valley's greatest concentration of major temples and historic buildings.
Here, on Patan's Durbar Square, stands the valley's greatest concentration of major temples because it is considered a holy site. 
mnli hypothesis: Here, on Patan's Durbar Square, stands the valley's greatest concentration of major temples because it is considered a holy site.  premise: Here, on Patan's Durbar Square, stands the valley's greatest concentration of major temples and historic buildings.