From the period of Zhabdrung and until the beginning of the 18th century, Bhutan was confronted with repeated external invasions from Tibet and internal opposition from the five groups (schools) of Lams. Continuous disputes, political conflicts, and wars necessitated the seat of religion and government – the Rinpung Dzong – to have its own guardian watchtower or Ta dzong, in addition to fortified structures to keep close watch on the movement of enemy forces and protect against their attack. Paro Ta dzong, the fortress of watchtower was thus built on the promontory of the eastern spur of Paro valley directly above Rinpung Dzong in 1649 by La Ngonpa Tenzin Drugdra, the first Paro Penlop or Governor of Paro, who later rose to prominence as the Second Druk Desi or Temporal Ruler of Bhutan from1656 to 1665. Tenzin Drugdra was born in Trongsa (Mangde) and was the half-brother of the great Zhabdrung Ngawang Namgyal, the founder of Bhutan.
La Ngonpa Tenzin Drugdra built the most unique architectural monument, with features unlike most other notable structures in the country. Nearly four centuries old, the building design is said to emulate the union of the sun and the crescent moon, which are considered an emblem of victory. The structure is unusual because of its circular ground plan with the central tower reaching a full height of seven stories. The impenetrable stonewalls are 2.5 meters thick, with arrow loops and oriel windows, thus fortifying the building with significant stability. Its strategic location provides a visual advantage for its intended defensive purpose with a panoramic view of the Paro from the hillock of Hungrel.
The construction was done with a highly evolved degree of masonry work, evident of skilled craftsmanship. The stone walls are constructed with stones in different sizes make for strong durable walls, and at different intervals massive stones are used to anchor and hold the masonry walls. In 1714, earthquake tremors occurred over a fifteen day period, and later in 1896, a very strong earthquake damaged many dzongs and temples. Paro Ta Dzong escaped all these historic damages due to its strong and durable structure, in particular the walls.
In the 17th century the Ta Dzong along with its primary purpose as a watchtower, also served as a supplies storehouse, and most importantly as the residence of Dzongpons (Governors). The networks of secret underground tunnels connecting it to the Rinpung Dzong served a dual purpose to source supply of water to the Ta Dzong from the Paro River and provide supplies to Rinpung Dzong in the event of war.
In 1872, Jigme Namgyel, Penlop or Governor of Trongsa sent his son, Gongsa Ugyen Wangchuck at the young age of 15 years to suppress the revolt instigated by Parob Tshewang Norbu (Governor of Paro) and Puna Dzongpon Ngodrub (Governor of Punakha). During the conflict Ugyen Wangchuck was taken prisoner and was held captive in the dungeons located on the ground floor of the Ta Dzong. A plot to assassinate him was uncovered, and foiled by his father Jigme Namgyel, and the building heralded the eventual triumph over his foes. Later in 1919, His Majesty Gongsa Ugyen Wangchuck was enthroned as the first hereditary monarch of Bhutan.