|Settled||1 June 1932|
|Established||29 December 2019|
|Reorganized||8 March 2021|
|• Body||Mariënburg City Council|
|• Administrator||Alda Carvalho|
|• Total||7 (permanent)|
Mariënburg (German pronunciation: [mariænboʊrg]), officially Municipality of Mariënburg (Portuguese: Município de Marienburgo) is the capital and largest settlement of the Province of Eichenham, with a population of 7 permanent residents. The municipality is the largest agricultural producer in the country, accounting for about 90% of the province's gross domestic product, and is the third largest contributing municipality to the national GDP after Malmünd and Minen. It is governed by a City Council composed of 4 life-long members appointed by the Administrator of the city, who is turn appointed by the Viceroy of Eichenham.
The municipality comprises Fazenda Carvalho, established after the purchase of the land by Geraldo Fernandes and Francisca Carvalho in 1932. Mariënburg was formally created as a municipality by the couple's great-grandson, Arthur van der Bruyn, when he took over the throne of the Kingdom of Ebenthal and annexed his family's holdings to the micronation. Initially, the municipality was named Sant'Anna in honor of the King's great-grandmother, Maria Sant'Anna de Oliveira, and in 2021 the name was changed to Bauernhof-Sant'Anna by the Luso-Germanic Cultural Commission, which again in 2023, under royal decree changed the name of the city to Mariënburg. Since its founding, the county has been the capital of Eichenham, formerly known as Geraldorf and Principality of Aldiva, having been the seat of the Aldivean monarchy headed by Geraldo and Francisca's daughter Princess Alda, Duchess of Eichenham.
Mariënburg is divided into 4 districts established according to its agricultural divisions. They are the District of Pomares (after orchards), Trigo (wheat), Rio das Velhas (the Old Crone River, in Ebenthal known as the Altendamenach River) and Fazenda (farm). Unlike all other cities in the country, Mariënburg has most of its territory (about 95%) and total population rural rather than urban. The entire local population, which includes Argentine immigrants, is employed in municipal and provincial agriculture. The immense amount of income generated by the municipality compared to its median population makes Mariënburg the municipality with the highest per capita income in the country.
The city was originally called Sant'Anna after Maria Sant'Anna de Oliveira, mother of José de Oliveira Filho, maternal grandfather of the King Arthur II of Ebenthal. The Sant'Anna and Oliveira families are native to the metropolitan region of Belo Horizonte, in Brazil, where the city lies enclaved. The name was changed to Bauernhof-Sant'Anna, where Bauernhof is "farm" in German, as part of the cultural Germanization project implemented by the Luso-Germanic Cultural Commission. In 2023 the name was changed to Mariënburg, a combination of the name Maria in German, Marien, as a way of honoring both Maria Sant'Anna and Maria Carvalho, grandmother of the King of Ebenthal, with the German toponymy burg.