The Roman amphitheatre in Windisch was built in the first half of the 1st century AD in the immediate vicinity of the Roman legion camp Vindonissa. It is the largest ancient amphitheatre in Switzerland.
During the reign of Emperor Tiberius (14 to 37 AD), when the Legio XIII Gemina was stationed in Vindonissa, a first wooden amphitheatre was built. It was destroyed by fire around 45 AD.
The camp was rebuilt of stone around 50 AD by Legio XXI Rapax and it has been preserved until today. The outer wall was 111 × 99 meters, the arena 64 × 52 meters. There was space for around 11,000 spectators.
Celje Castle was once the largest fortification on Slovenian territory. The first fortified building on the site (a Romanesque palace) was built in the first half of the 13th century by the Counts of Heunburg from Carinthia on the stony outcrop on the western side of the ridge where the castle stands. It had five sides, or four plus the southern side, which was a natural defence. The first written records of the castle date back to between 1125 and 1137; it was probably built by Count Gunter. In the western section of the castle, there was a building with several floors. Remains of the walls of this palatium have survived. In the eastern section, there was an enclosed courtyard with large water reservoirs. The eastern wall, which protects the castle from its most exposed side, was around three metres thicker than the rest of the curtain wall. The wall was topped with a parapet and protected walkway.