Zhabdrung Ngawang Namgyal was one of the greatest builders of Dzongs in Bhutan and to consolidate his newly acquired domain in western Bhutan and to defend himself from both the internal foes and external enemies he started the constructions of six Dzongs.

The first Dzong that he undertook to construct was the Simtokha Dzong. The location has a great historical significance. The present place where the Dzong stands was the crossroads of the three prominent western regions of Sha (Wangduephodrang), Wang (Thimphu) and Pa (Paro). The intersection was marked by three stones that belonged to the people of Punakha, Thimphu and Paro. In the middle of these three stones was a piece of land known as Sem – to kha or Sem – Dokha with a temple built on it.

This temple was later gifted to Zhabdrung by Lam Pangka Shong. History says that a prophecy was made by one Tibetan Lama Known as Lama Zhang that Zhabdrung Ngawang Namgyel after his arrival to Bhutan would build a Dzong at the junction of three western lands. As a gesture of fulfilling the prophecy and soliciting the offer of Lama Pangka Shong, Zhabdrung decided to build the Dzong.

The area was inhabited by many demons and legend has it that the particular place where Zhabdrung decided to build the Dzong was occupied by a demon harming the travelers who often stayed during the night. Zhabdrung visited the place and subdued the demon, banishing her into the rock on the hill where the present Dzong is located. The Dzong was constructed enclosing the rock ensuring the imprisonment of the demon. Hence the Dzong derived its name as Simtokha from the word sinmo (demon), Do (stomach), Kha (on) – the Dzong on top of the demon’s stomach.

At the age of 36, in 1629 corresponding to the 11th Rabjung and Earth Snake Year of the Bhutanese calendar, he laid the foundation of the Dzong. The construction of the Dzong was undertaken by Tango Chhoje Mipham Tshewang Tenzin with assistance from Zhabdrung’s devotees and disciples.