The Toome Hill, rising above Old Town, has always been strategic military position. Tartu's original settlement, Tarbatu, was established here in 600AD, and if you trace the hill's outline on a map, you can still see the shape of fortifications built here in the 17th and 18th centuries.
The western part of the hill is clearly dominated by the ruins of the 13th-century cathedral (Toomkirik) that has been decaying since the Livonian War (1558-1583). The sanctuary, which is still in a quite good condition today, accommodates the University’s history museum. Here you can get a broad overview of academic research and teaching in Tartu.
The old observatory of Tartu was constructed in 1811. It was the most modern one in Europe in the 19th century.
References:The Château de Foix dominates the town of Foix. An important tourist site, it is known as a centre of the Cathars. Built on an older 7th-century fortification, the castle is known from 987. In 1002, it was mentioned in the will of Roger I, Count of Carcassonne, who bequeathed the fortress to his youngest child, Bernard. In effect, the family ruling over the region were installed here which allowed them to control access to the upper Ariège valley and to keep surveillance from this strategic point over the lower land, protected behind impregnable walls.
In 1034, the castle became capital of the County of Foix and played a decisive role in medieval military history. During the two following centuries, the castle was home to Counts with shining personalities who became the soul of the Occitan resistance during the crusade against the Albigensians.