Traditionally the Lithuanian castles were wooden hillforts. None of them survived to this day, but many castle hills remain, some dating to the Bronze age. 5 of them are in Kernavė, the UNESCO-inscribed former capital (Aukštaitija region). There is an undergoing project to rebuild a wooden castle in Anykščiai (Aukštaitija).
Medieval brick castles were constructed in strategic locations along the rivers and near the political heartland of the country (Vilnius). The remains of the Vilnius and Kaunas castles are in the Old Towns and symbolically important. The reconstructed Trakai Island Castle is the most popular day-trip from Vilnius. Castle remains exist in Medininkai (East of Vilnius) and in Klaipėda. The Klaipėda castle constructed by the Teutonic knights, the arch-enemy of Lithuanians at the time. At this time entire cities were walled, but save for the few fragments the walls were destroyed in the 19th century. Some of the Grand Duchy of Lithuania castles are now in Belarus and Ukraine.
The end of the Teutonic crusades in the 15th century permitted Lithuanian nobility to move from their castles to newly-built opulent manors. The richest ones covered tens of hectares and included many buildings and extensive gardens. Poorer nobles lived in wooden manors that differed from peasant homes only in size and architectural details. Some of the nobility palaces of 17th-19th centuries are built to resemble medieval castles. Three such castles are built near Nemunas west of Kaunas. The manors make an important part of the Lithuanian countryside as there are some 800 of them remaining, in different states of repair. The era of the manors ended with the land reform of 1923 and was completely struck down in 1944 with the nationalization and mass looting by the Soviet soldiers. As many of the manors eventually had a town built around them, see the page on towns of Lithuania to learn more about non-castle type manors.
The need for defense did not disappear with the increasing peace but artillery advances rendered castles obsolete. They have been replaced by bastion fortresses such as Biržai castle, at the time of construction among the most modern in Europe.
Industrial city growth replaced the idea of a single fortress to that of a massive ring of forts. In the 19th century the size of fortifications reached its pinnacle, with the Kaunas fortress absorbing the entire Lithuania's second largest city to such extent that the ruling Russian Imperial officials exclaimed: "There is no [longer a] Kaunas city. There is only Kaunas fortress". All the further city improvements were meant to serve the fortress and soldiers/officers made up 28% of city dwellers. Still surrounding the city the Kaunas fortress is one of the best-preserved examples of such 19th-century fortresses in the world.
20th-century mobile warfare and air force advances made such fortresses obsolete and they were supplanted by compact hidden installations, manned by several soldiers each. Such buildings may be found in woods near Vilnius (built by the Poles in the 1930s) and elsewhere (built by the Soviets). In the forests, you may also see modest secret bases of Lithuanian anti-Soviet partisans. Arguably the most interesting military installation of the 20th century is the underground Plokštinė Soviet nuclear missile base in Samogitia.