Sisak Fortress

{{Short description|Castle in Croatia}}

{{Use dmy dates|date=August 2019}}

{{citation style|date=June 2017}}

{{Infobox military installation

| name = Sisak Fortress

| native_name = Tvrđava Sisak
Stari grad Sisak

| location = Sisak, Croatia

| coordinates = {{coord|45.470531|16.386222|type:landmark|display=inline,title}}

| image = Tvrđava.sisak.JPG

| caption = Sisak Fortress from the south

| map_size = 200

| type = Lowland fortress

| built = 1544-1550

| builder = Petar de Mediolanus

| controlledby = Bishop of Zagreb; from the 17th century: several other possessors

| materials = brick, hewn stone (ashlar)

| height =

| used =

| condition = partially preserved

| ownership =

| open_to_public = Sisak Town Museum

| embedded = {{Infobox historic site

| embed = yes

| designation1 = Croatia Cultural

| designation1_offname =

| designation1_number = Z-3487{{Cite web |title=Stari grad |url=https://registar.kulturnadobra.hr/#/details/Z-3487 |access-date=2023-05-28 |website=Registar Kulturnih Dobara}}

| designation1_type = Protected cultural good

}}

}}

The Sisak Fortress ({{langx|hr|Tvrđava Sisak}} or {{lang|hr|Stari grad Sisak}}) is an early modern lowland fortification built on the bank of the Kupa River before its mouth into the Sava. It is situated in the suburb of modern-day city of Sisak, Sisak-Moslavina County, central Croatia.

It is a triangle-shaped structure, mostly made of brick and supported by stone parts. Each corner of the fortress is reinforced with a round tower covered by conical roof. Towers are connected by the more than 30 metres long thick walls with loopholes. Being on the river bank, the fortress has a natural line of defense from the west-southwest, while the other sides are partially protected by the Sava River in the immediate vicinity, flowing southeast.

In its history, the Sisak Fortress was damaged several times and subsequently subjected to renovations. Generally, although it needs a renewal today, it is in good condition. It houses the local town museum.