The architecture of these buildings has been attributed, to a large extent, to two Danish architects named Theophilus and Christian Hansen.

Christian Hansen was born in Copenhagen and graduated from the Fine Arts Academy of Copenhagen in 1816, at just 13 years old! A notable statement of his goes as follows: "As one delves deeper into his art, the more he feels it and the desire of looking for it at the place of his birth only grows stronger and stronger. Something similar has happened to me. My desire to travel to Greece has grown so much in me, that it has reached the point to be my unique purpose." And so he did.

After he continued his artistic career with a trip to Italy in 1833, he came to Athens, which had recently gained its independence from the Ottoman occupation after 400 years. The aim was to transform the latter city into a metropolis, like other European capitals. The talented Dane then won the favor of King Otto and was appointed the official Architect of the King. He initiated the constructions to be carried out initially on his own, yet later received help from his brother, Theophilus.

One of Christian's most emblematic buildings that are worth mentioning first is the National & Kapodistrian University of Athens. Built in a neoclassical style completely from marble, it is a paradigm of exquisite architecture, as it renders anyone who visits it, speechless. It is one of the three characteristic buildings of the historical center of Athens - together with the National Library of Greece and the Academy of Athens.

However, these structures are not the only ones that Christian contributed to their construction by designing the architectural plans. The Anglican Church of St. Paul (with gothic elements and the classic Victorian style), numerous temples in the Athenian capital, the Kantakouzenos building in Athens, the Mint, the Eye Clinic (Ophthalmiatreio), the Crown Prince's Palace, and the Hotel built for Österreichischer Lloyd owe their existence to his brilliant designs. Moreover, in collaboration with the German architect Eduard Schaubert, they excavated and rebuilt the Temple of Athena Nike on the Acropolis.

After the uprising that occurred in September of 1843 in Athens, the wave of  nationalism made it difficult for foreigners to find work in Greece. In 1851, Christian Hansen returned home after almost 20 years of living abroad.

His brother, Theophilus Hansen, was also an internationally successful architect, with a range of work limited to Athens and Vienna. Theophilus, was originally inspired by the ancient architecture of Rome and, after the end of the 18th Century, from classical Greece. This gave his works a character that was more strict and austere, with its foundations based on the Enlightenment.

The Danish influence filled him with stimuli that led him to study neoclassicism. The combination of Philhellenic groups, Dutch intellectuals and the moving of his brother into the Athenian capital, led to the formation of the architect, who bejeweled our city with his magnificent buildings. The city of Athens seemed ideal for Theophilus who had the opportunity to study, plan, mirror and restore ancient monuments. He used them as templates in his creations of architecture, that later distinguished him for his spiritual growth while in Athens.

In 1838, Theophilus arrived in the Greek capital, while Christian had already undertaken the design and supervision of the construction of the National University. It is the first project in which Theophilus participated as an assistant to his brother.

Theophilus owes to Athens, the well-founded basis of his multiple projects. His art is characterized as a tireless, creative and free of molds - with a style that reflects freedom and encompasses traits of his personality. In 1846, he undertook the designing and planning of the construction of the National Observatory on the Hill of the Nymphs. This building was the last work he oversaw in Athens before leaving for Vienna in 1846. It is the building that challenged Theophilus Hansen most, as he had to overcome a number of technological problems, and whose construction is due to the sponsorship of Baron George Sina.

Theophilus left Athens and finally settled  in Vienna, where he quickly became famous.