Annaburg is a three-story Neo-Classical Revival–style manor in Manassas built between 1892-1894 as the summer home to the family of Robert Portner, a German immigrant who became a prominent brewer and inventor in Northern Virginia. Designed by Gustav Friebus, an architect who worked on the Washington Monument, Annaburg incorporates locally made brick and locally sourced brownstone. A large, tiled landing—originally part of a wraparound porch—extends from the front entrance. When completed, the house also integrated new technologies of the day such as electricity, indoor plumbing, and the novelty of mechanical air conditioning. Portner patented a method for cooling and purifying air, a system he also installed in his Alexandria brewery. Annaburg’s design draws on elements from Portner’s favorite European architecture including painted ceiling frescoes, imported Italian marble fireplace mantles, and ornamental statuary from Greece. The Portners hosted various public events at the 2,000-acre estate until 1919, after which the property fell into disrepair until the family sold it in 1947. Annaburg housed a nursing home starting in the 1960s and the City of Manassas acquired it in 2019. A tree-lined drive leading up to the house and other landscaping remain from the Portner era. At the time of listing, the city was developing the 3.7-acre Annaburg property into a public park.