Holy Langhorne Canal

The Holy Langhorne Canal was the longest canal on Safehold, at 1,800 miles. It connected the Sabana River with West Wing Lake, and travelled through muliple nations. It crossed from Sabana, through the Earldom of Usher, the Duchy of Ernhart, Sardahn (twice), the Barony of Charlz, and finally ending in the Tarikah Province of the Republic of Siddarmark. (map)

It provided a logistics pipeline all the way from the Temple Lands to Lake City. (MTAT)

During the Siddarmark Civil War, it allowed the Army of God to transport almost half a million into Tarikah and Westmarch Provinces. (MTAT)

History
The Holy Langhorne Canal had been dug by Pei Shan-wei’s terraforming crews even before the Day of Creation. It was amongst the first canals on the planet, and during the Church's war with Charis, it allowed the mainland realms  to transport the tonnages of materials they needed for its military buildup after Charis closed the seas to them. (MTAT)