The imposing building was designed by Alexandros Georgantas and was built in 1859-1861. It is a two-storey building, built with marble and its sides look like towers. The design of the building reminds us of the constructions of Stamatis Kleanthis. He was the designer of the first urban plan of Athens, in cooperation with the Bavarian Ed. Schaubert on behalf of the Duchess of Plakentia in Penteli.
A section of the Customs office was destroyed by bombing during the war and was then rebuilt following the original plan. A dock was also built which is still used till nowadays for the ships which require customs control.
A few years earlier, in 1834-1839, the transit warehouses were designed by I.B Erlacher, under the supervision of Wilhelm von Weiler. The building has a total length of 122 m., with two wings arranged symmetrically. Each wing has seven warehouses. There used to be a portico with large arched openings, which are now closed. The barges anchored beside the building by the sea, and unloaded their cargo directly in the portico.
The warehouses were covered with cylindrical vaults. The only entrance was from the portico and there were arched windows on the back side. The floor in the central part of the building was built a few years later while the rest of the building was built together with the neighboring Customs Office in 1859-1861.
Since the interwar years, the warehouses had ceased to perform their original function. Arrangements were made for the installation of public services (Port Authority), restaurants etc. In 1994 four warehouses on the south ward were taken to house the Cyclades Art Gallery, which hosts exhibitions and collections (entrance from the back side of the building).
