Similar to Sandersdorf, the Romanesque fortified church in Thalheim is the oldest building and, with its 21m high tower, also the highest and can be seen from afar. It was built around 1150-1170 from heavy porphyry rubble and some boulders. With a width of 10 m and a length of 25 m, the church is divided into four parts: transverse west tower, nave, altar choir and apse, although it remains single-nave and the nave adjoins the tower at the same width. Romanesque architectural features, such as the joint technology in the tower and the pairs of transoms in the three arches, are still clearly visible.
Some remarkable individual parts are noticeable on the exterior, such as the corner stones of the gable walls or the top of the apse roof, which still retains its old late medieval covering in monks and nuns.
This top is made of stone and ends in a stone button, above which an openwork stone slab closes an opening in the gable of the chancel. Of course, the button is only semicircular in front of the gable wall. The stone slab is square and shows a diagonally placed cross. This button and the stone slab give the otherwise sparse building a very attractive effect. All of these profiles and shapes show that they were carved in the late Romanesque period. The lack of decoration and the high, narrow windows clearly show why this type of building is also called a fortified church: in times of war, the church building often served as a shelter for the local residents.
The Thalheim church has preserved these features of the Romanesque era like no other in the Bitterfeld district. Only a few renovations changed its appearance. The biggest renovation took place in 1891/92: the entrances on the north and south sides of the church were bricked up and moved through the tower to the west. Since then, visitors have found the saying above this portal:
"Here is nothing but God's house, here is the gate of heaven" from Genesis.
The tower houses two historical bronze bells from 1617 (diameter 77 cm / 280 kg) and 1679 (diameter 94 cm / 600 kg), which are richly decorated. In March 2001 both bells received new yokes and clapper. On November 3, 2000, a new third bell was cast for Thalheim in Lauchhammer.
The nave appears very high due to its barrel ceiling and two galleries. In 1950, the small winter church was set up on the south side. To do this, the rows of pews had to be divided and the aisle placed in the middle.
The chancel has a flat wooden coffered ceiling. It contains the stone pulpit and the baptismal font from 1677. It is made entirely of wood, octagonal, two-part, portable and therefore a true rarity. On the upper edge of the stand there is the dedicatory inscription: "The noble-born woman Anna Helena, née von Lüderitz, widow of Zanthier, had this work made and set as it is, in holy honor to God, for the blessed use of this church. Remember me, my God, for the best! - 1677". The baptismal font was repaired in 1998 by Angela Günther, a qualified restorer from Dessau. In the apse there is the altar bar with a slab made of red sandstone in which consecration crosses are carved.
The altarpiece was made in 1692 by the painter Simuta and donated by Georg Heinrich von Zanthier. It is divided into two parts, with the lower part being the older one. The three oil paintings are painted on wood and depict the last supper of Jesus with the 12 disciples (bottom), the crucifixion of Jesus (middle) and Jesus' resurrection (top). The pictures are bordered on the right and left by a pair of columns. To the left of the lower picture is the figure of the evangelist John with his symbol of the eagle and to the right of the evangelist Luke with his symbol of the bull. On the left side there are ears of wheat and cornflowers, on the right side there are grapes and vine leaves as symbols of the Lord's Supper that adorn the altar. The saying from the 11th chapter of 1 Corinthians on the predella also refers to the Lord's Supper: "As often as you eat this bread and drink this cup, you should proclaim the Lord's death until he comes." The essay was restored in the Erfurt church workshops in 1998-1999 and, together with the baptismal font, was ceremonially handed over again in a celebratory service on Ascension Day in 1999.