Opposite the Alexander Nevsky Cathedral is the oldest Orthodox church in Sofia - the Basilica of St. Sophie.
The name of the capital city of Bulgaria mostly derives from this church (The previous name originated from the Greek word Serdika). It is the largest Byzantine church outside the borders of Constantinople; built in the 6^th century A.D. during the reign of Justinian. The materials used to build the church are dated back to the 5^th and 6^th centuries A.D. Under Ottoman rule, the church was rebuilt into a mosque, but in the 1800s the church ceased to be used due to structural damage caused by multiple earthquakes. From the year 1900 a new construction project began, resulting in the Basilica returning to its original state as an Orthodox church. After multiple restoration projects, the St. Sofia Basilica opened its doors once again during the year 2000. Today, the likeness of the church is made to very closely resemble that of its original appearance during the Middle Ages. St Sofia represents the divine wisdom not through its saintly icons in the church, but through its namesake, who stands on the top of the church above three other women, depicting: faith, hope, and love. She is an important figure in the lives of the residents of Sofia.

The first wall was made of brick and sits on a 2 meter foundation of stone. It stood at a height of around 8 or 9 meters, with a width of 2.2 meters. About 50-60 meters distance from each other, towers built for defensive purposes rise 2-3 meters above the wall. The remains of the first wall were then replaced by a new second wall in during the 4^th century. The construction of this second wall utilized an ancient Roman building technique called “opus mixtum”, with 4 rows alternating between brick and stone. The new walls follow the form of the original, with the addition of stairs which enhance the thickness of the walls. In some places there were also added side exits called posterns.

During the reign of Emperor Justinian (527-566), construction of the existing wall was set in motion. This wall was surrounded with yet another barrier with a width of 1.8 meters. New triangular towers were placed between the existing ones. These triangular towers were located near the three main pentagonal entrances. Around this was built a third wall 2 meters thick with a distance of 20m from the main rampart.

Part of this wall, which was situated on the eastern border of the ancient city, was discovered under Alexander Dondukov Boulevard. They were found under the Presidential office and the Ministry building. Some reconstruction work was carried out in 1997-1999 in order to allow visitors to see the fragments of the past that are buried underneath the capital.

Coming out of the underground passage, you will have the opportunity to observe the Church of Saint Petka of the Saddlers, dating from the 15th century that was created under Ottoman rule with the donations from the Brotherhood of Saddlers in Sofia, hence its name.

The church was dedicated to the martyr Petka Ikoniyska. It was built on top of the ruins of an 11th century Roman temple. During this time, construction of churches was allowed, with the restriction that their height was not allowed to exceed the height of a soldier on horseback. Thus, many churches were partially constructed underground. This is a great example of one of these structures. There are some visible traces of antique frescoes in the semicircular arches (part of a three stage of a mural painted in the 15th, 17th, and 19th centuries. There is a theory suggesting that the church is the resting place of Vasil Levski, a national hero and symbol of resistance, who was arrested and hung in Sofia during 1873. A vestige of the past, miraculously preserved through time among the hulking communist buildings, this church is a great example of the rich and diverse heritage of the capital.