In 1433 , Gyalpo built eight bridges in eastern Bhutan .
The Tibetan saint and bridge - builder Thangtong Gyalpo originated the use of iron chains in his version of simple suspension bridges .
In 1433 , Thangtong Gyalpo built eight bridges in eastern Bhutan .
The Tibetan saint and bridge - builder Thangtong Gyalpo originated the use of iron chains in his version of simple suspension bridges .