Schloss Eisenberg, Renaissance castle in Eisenberg, Germany.

Schloss Christiansburg in Eisenberg is a Baroque three-wing complex built 1677–1692 by architect Wilhelm Gundermann for Duke Christian of Saxe-Eisenberg, incorporating the surviving west wing of the medieval castle and Renaissance palace. Its fronts are plain, with a red sandstone portal carrying a balcony on Corinthian columns; red sandstone also frames the windows, and the interiors have ceilings decorated by Italian masters.

A castle has stood here since the 12th century, guarding trade routes and ringed by a wall and moat. In 1589 the "Neue Küche" was added; of the medieval castle and Renaissance palace only the west wing survives. Duke Christian of Saxe-Eisenberg had builder Wilhelm Gundermann of Altenburg remodel it into a Baroque three-wing complex in 1677–1692, with the palace church St. Trinitatis added on the east side in 1679–1692.

The castle church, St. Trinitatis, was consecrated in 1692 and has an octagonal tower with pilasters above its projecting choir. Between 1958 and 1960 it was adapted as a concert hall. The nearby Mohrenbrunnen fountain of 1727 recalls the town coat of arms, which shows the head of a Moorish page with a band over his eyes.

The castle stands south of Eisenberg's old town on a slope falling away to the south, near the junction of the B7 with roads to the surrounding villages. The building now houses offices of the Saale-Holzland district administration, so visitors see it from outside; the two adjoining parks, with their pavilion and tulip trees and planes near the east exit, are open to walkers.

A stone beside the castle passage bears the year 1589 and the letters VDIMIAE, initials of the Schmalkaldic League motto "Verbum Domini manet in aeternum" (the Word of God remains in eternity). It is a surviving trace of the medieval castle and Renaissance palace, of which only the west wing still stands.