It was the first time Ngo Mon, as the gate is known in Vietnamese, was cleaned using modern technology. The company used high-pressure steam to remove dirt and biological contaminants that had accumulated over the years.

The cleanup was headed by Thorsten Marco Mowes, a Karcher expert in cleaning and sanitation technology, and Andrea Teufel, a German conservation expert who has been working on the Hue heritage site for 15 years.

They had to use ladders to reach the upper parts of the structure.

Thorsten Marco Mowes instructs an employee.

The German expert also personally took part in the operation, which returned the bricks to their original color.

Many of the nearly-200-year-old gate's bricks have regained their bright red color following the cleanup.

Many of the nearly 200-year-old gate's bricks (L) have regained their bright red color after 15 days.

The German company will conclude the cleanup and hand over the gate to Hue authorities on Friday.

The imperial citadel is a part of Hue’s Complex of Monuments, a UNESCO world heritage site.

It has many relics from the era of the Nguyen Dynasty (1802-1945), the last feudal rulers of Vietnam, and is among the top historical and tourism sites in the country.