Today, orthodoxy is the major religion in Romania, but it has not always been so. The local Orthodox Church received official status in Austria-Hungary (Romania was part of it back then) only in the middle of the 19th century. Sibiu was a major religious center with a synagogue, Catholic and Lutheran churches. Therefore, it was decided to build the main Orthodox cathedral of Romania in this city. To do this, 8 residential buildings and a small Greek Orthodox church on Mitropoliei Street had to be demolished.

The beginning of the 20th century was marked by a flourishing interest in Byzantium, especially since Romania has always been at the crossroads of Western and Eastern cultures. Thus, the most "Byzantine" project was chosen among the 30 designs proposed to the Consistory of the Archbishop. This chosen project was reminiscent of Hagia Sophia in Istanbul. In 1906, the temple was consecrated and started housing the cathedra of the Archbishop of Sibiu and the Metropolitan of Transylvania. Besides, it began to be called the cathedral.

Two 45-meters-high towers rush off to the sky, a huge dome with a diameter of 15 meters and a height of 35 meters covers the nave, four smaller towers are decorated with 1.5-meter crosses. The exterior walls are built of red and yellow bricks, the rows of which alternate and create a pattern similar to a traditional Romanian carpet.

Inside, the cathedral looks even more impressive than outside. It seems that all the main colors of Romania are collected here: blue, like the sky, and gold, like fields of wheat. All the frescoes in the cathedral and the wooden, gold-covered iconostasis were made by the Transylvanian master Octavian Smigelschi. He graduated from the Academy of Fine Arts in Budapest and studied in Italy. Before starting to paint the cathedral, he visited dozens of ancient churches in Romania, Moldova, and Western Ukraine. As a result, the Holy Trinity Cathedral got a magnificent decoration of mosaics, stained-glass windows, and frescoes (the largest, Christ Pantocrator, adorns the vault of the main dome). The images do not seem old: they combine canonicity and a touch of modernism. There has always been the contrast between the Holy Trinity Cathedral, an islet of Byzantium, and the surrounding Saxon-style houses. But it only increases the charm of the medieval city.