The Trans-Iran­ian Rail­way con­nects the Caspi­an Sea in the north­east with the Per­sian Gulf in the south­west cross­ing two moun­tain ranges as well as rivers, high­lands, forests and plains, and four dif­fer­ent cli­mat­ic areas. Start­ed in 1927 and com­plet­ed in 1938, the 1,394-kilometre-long rail­way was designed and exe­cut­ed in a suc­cess­ful col­lab­o­ra­tion between the Iran­ian gov­ern­ment and 43 con­struc­tion con­trac­tors from many coun­tries. The rail­way is notable for its scale and the engi­neer­ing works it required to over­come steep routes and oth­er dif­fi­cul­ties. Its con­struc­tion involved exten­sive moun­tain cut­ting in some areas, while the rugged ter­rain in oth­ers dic­tat­ed the con­struc­tion of 174 large bridges, 186 small bridges and 224 tun­nels, includ­ing 11 spi­ral tun­nels. Unlike most ear­ly rail­way projects, con­struc­tion of the Trans-Iran­ian Rail­way was fund­ed by nation­al tax­es to avoid for­eign invest­ment and con­trol.