Viljandi castle was one of the strongest castles in Livonia. The construction was started 1224 under Teutonic Order in place of a former hillfort. The crusaders of Sword Brethren conquered the hill fort at the place of later main castle in 1223. A year later, construction of stone fortifications started. Viljandi was chosen as the high seat of the order.
The convent house, a typical form of castle of Teutonic Knights, was erected late 13th – early 14th century. In the following centuries the castle was extended and fortified further. It was badly damaged in the Polish-Swedish wars in early 17th century and not repaired any more. In 18th century, the ruins were used for quarrying stones for construction work in Viljandi.
The first excavations in the castle were performed in 1878–1879. In recent decades, these have turned to almost yearly events. Currently the ruins form a popular resort area just outside of central Viljandi. An open-air stage is located in the former central courtyard.
Reference: Wikipedia
The Baths of Caracalla were the second largest Roman public baths, or thermae, in Rome. It was built between AD 212 and 217, during the reigns of Septimius Severus and Caracalla. They would have had to install over 2,000t of material every day for six years in order to complete it in this time.
The baths remained in use until the 6th century when the complex was taken by the Ostrogoths during the Gothic War, at which time the hydraulic installations were destroyed. The bath was free and open to the public. The earthquake of 847 destroyed much of the building, along with many other Roman structures.
The building was heated by a hypocaust, a system of burning coal and wood underneath the ground to heat water provided by a dedicated aqueduct. It was in use up to the 19th century. The Aqua Antoniniana aqueduct, a branch of the earlier Aqua Marcia, by Caracalla was specifically built to serve the baths. It was most likely reconstructed by Garbrecht and Manderscheid to its current place.
In the 19th and early 20th century, the design of the baths was used as the inspiration for several modern structures, including St George's Hall in Liverpool and the original Pennsylvania Station in New York City. At the 1960 Summer Olympics, the venue hosted the gymnastics events.