The Antakalnis fortifications are ammunition bunkers of the Vilnius garrison of the Polish Army, built in 1924–1926. Having occupied Vilnius, Poland decided to turn the city into a modern fortress and built defensive fortifications. The fortifications built in the first half of the 20th century varied – some above ground, others under hills, some even with several storeys or long tunnels. These bunkers are a typical relic of war – or rather of preparing for war. When the Germans attacked the city from the other side in 1939, the whole defence became worthless. The fortifications never served their intended purpose, and not a single shot was fired from them. During the war and afterwards the bunkers were used as shelters or storehouses. Pavilniai Regional Park has many remains of fortifications. In Antakalnis, on the Sapieginė spur, five bunkers with ten entrances survive. One of the bunkers has two storeys. The underground rooms are surrounded by very narrow tunnels or ventilation ducts. Near the bunkers there is a stone-paved road, and there were once narrow-gauge railway tracks as well. The bunkers have now been tidied up and the entrances fitted with grilles. The Antakalnis bunkers have been designated a habitat of European importance (included in the Natura 2000 network), protecting a wintering site of a bat species, the western barbastelle. For this reason, visiting is prohibited during the bats' hibernation period (September–April). In 2008 the Antakalnis bunkers were entered in the Register of Cultural Property of the Department of Cultural Heritage as a landscape, rare architectural and engineering object. Not far from the Antakalnis bunkers, within the Ancučiai Landscape Reserve, are the Kojelavičius fortifications. They are far more complex and interesting than the Antakalnis bunkers. Large bat colonies also winter here, although this area is not protected. There are also remains of fortifications near the Pūčkoriai outcrop and at the end of Rasų Street (now an area of private houses).