The castle was probably built in the 13th century most likely in place of an ancient Estonian stronghold. The bailiwick of Karksi was first mentioned in 1248. The stronghold had a chapel dedicated to Apostle Peter. The first reference was made to a local clergyman in 1298. The present stone church, very simple in design, was built in the same place between 1773 and 1778. St. Peter’s Church is in the ruins of Karksi castle. The tower of the church is leaning, the inclination of the tower’s top is 205 cm at the moment. In 1994 it was decided to save the tower using complicated "construction surgery" developed while stabilizing structures in the old town of Tartu. Eight 10- metre-tall bored piles along with concrete beams penetrating foundations form a new bearing surface for the tower. As a result, the further leaning of the tower has stopped.
On the way which takes you to the stronghold, in the former cemetery of the Knights of the Order of the Sword, stands a nice Baroque chapel among trees, built in the early 18th century by Field Marshal George Reinhold von Lieven, the owner of the Karksi manorial estate. The coats of arms of the Lievens and the Mannteuffels have been fixed to the chapel doors. The chapel, similarly, was built with one side on the former foundation and therefore is somewhat leaning. The buildings of the Karksi manor have perished.
The Porta Nigra (Latin for black gate) is the largest Roman city gate north of the Alps. It is designated as part of the Roman Monuments, Cathedral of St. Peter and Church of Our Lady in Trier UNESCO World Heritage Site. The name Porta Nigra originated in the Middle Ages due to the darkened colour of its stone; the original Roman name has not been preserved. Locals commonly refer to the Porta Nigra simply as Porta.
The Porta Nigra was built in grey sandstone between 186 and 200 AD. The original gate consisted of two four-storied towers, projecting as near semicircles on the outer side. A narrow courtyard separated the two gate openings on either side. For unknown reasons, however, the construction of the gate remained unfinished. For example, the stones at the northern (outer) side of the gate were never abraded, and the protruding stones would have made it impossible to install movable gates. Nonetheless, the gate was used for several centuries until the end of the Roman era in Trier.
In Roman times, the Porta Nigra was part of a system of four city gates, one of which stood at each side of the roughly rectangular Roman city. The Porta Nigra guarded the northern entry to the Roman city, while the Porta Alba (White Gate) was built in the east, the Porta Media (Middle Gate) in the south, and the Porta Inclyta (Famous Gate) in the west, next to the Roman bridge across the Moselle. The gates stood at the ends of the two main streets of the Roman Trier, one of which led north-south and the other east-west. Of these gates, only the Porta Nigra still exists today.
In the early Middle Ages the Roman city gates were no longer used for their original function and their stones were taken and reused for other buildings. Also iron and lead braces were broken out of the walls of the Porta Nigra for reuse. Traces of this destruction are still clearly visible on the north side of the gate.
After 1028, the Greek monk Simeon lived as a hermit in the ruins of the Porta Nigra. After his death (1035) and sanctification, the Simeonstift monastery was built next to the Porta Nigra to honor him. Saving it from further destruction, the Porta Nigra was transformed into a church: The inner court of the gate was roofed and intermediate ceilings were inserted. The two middle storeys of the former gate were converted into church naves: the upper storey being for the monks and the lower storey for the general public. The ground floor with the large gates was sealed, and a large outside staircase was constructed alongside the south side (the town side) of the gate, up to the lower storey of the church. A small staircase led further up to the upper storey. The church rooms were accessible through former windows of the western tower of the Porta Nigra that were enlarged to become entrance doors (still visible today). The top floor of the western tower was used as church tower, the eastern tower was leveled, and an apse added at its east side. An additional gate - the much smaller Simeon Gate - was built adjacent to the East side of the Porta Nigra and served as a city gate in medieval times.
In 1802 Napoleon Bonaparte dissolved the church in the Porta Nigra and the monastery beside it, along with the vast majority of Trier"s numerous churches and monasteries. On his visit to Trier in 1804, Napoleon ordered that the Porta Nigra be converted back to its Roman form. Only the apse was kept; but the eastern tower was not rebuilt to its original height. Local legend has it that Napoleon originally wanted to completely tear down the church, but locals convinced him that the church had actually been a Gaulish festival hall before being turned into a church. Another version of the story is that they told him about its Roman origins, persuading him to convert the gate back to its original form.
In 1986 the Porta Nigra was designated a World Heritage Site, along with other Roman monuments in Trier and its surroundings. The modern appearance of the Porta Nigra goes back almost unchanged to the reconstruction ordered by Napoleon. At the south side of the Porta Nigra, remains of Roman columns line the last 100 m of the street leading to the gate. Positioned where they had stood in Roman times, they give a slight impression of the aspect of the original Roman street that was lined with colonnades. The Porta Nigra, including the upper floors, is open to visitors.