Daugavgrīva Castle was originally a monastery converted as a fortress by Swedish in the 17th century. Today there are no remnants of the medieval castle above the soil.
In 1208 there was a Dünaburg castle built by the Teutonic Knights which initially served as a monastery. The Swedish fortress of Dünamünde, designed in a Dutch style by General Rothenburg in 1641, replaced the ruined Daugavgrīva Castle by 1680. In 1695 the Commandant was captain Heinrich Nicolaus Rüdinger, forefather of future Patriarch Alexy II of Russia. Rüdinger was knighted by Charles XI of Sweden. Joachim Cronman later became the Commandant and he died on March 5, 1703.
After the fortress was seized by the Russians they reconstructed it. Regent Anna Leopoldovna of Russia, her husband Anthony Ulrich, and her son Ivan VI were incarcerated in Dünamünde in 1742. A local Lutheran church was rebuilt into the Orthodox Church of the Saviour's Transfiguration in 1775. The Russian government renamed the fortress, where only Russian soldiers were living, to Ust-Dvinsk in 1893. They had its fortifications completely reconstructed prior to World War I. During the war Ust-Dvinsk was bombarded by the Schütte-Lanz Airship SL 7 of the German Army. After the fortress was taken by Imperial Germany, it was inspected by Emperor Wilhelm II in 1917. The Latvian government, however, demolished much of the fortifications several years later. During the Cold War Ust-Dvinsk was a base for Soviet troops. The site is now known in Latvian as Daugavgrīva. There is a functional lighthouse at Daugavgrīva which was originally built in 1818. It was rebuilt in 1863, 1920, and after World War II.
Nowadays entrance in the area of castle goes along the northeastern corner. Still there is partly visible the old road which was leading from northeastern tower around the forepart of the castle up to the southeastern corner.References:
Sirmione castle was built near the end of the 12th century as part of a defensive network surrounding Verona. The castle was maintained and extended first as part of the Veronese protection against their rivals in Milan and later under the control of the Venetian inland empire. The massive fortress is totally surrounded by water and has an inner porch which houses a Roman and Medieval lapidary. From the drawbridge, a staircase leads to the walkways above the walls, providing a marvellous view of the harbour that once sheltered the Scaliger fleet. The doors were fitted with a variety of locking systems, including a drawbridge for horses, carriages and pedestrians, a metal grate and, more recently, double hinged doors. Venice conquered Sirmione in 1405, immediately adopting provisions to render the fortress even more secure, fortifying its outer walls and widening the harbour.
Thanks to its strategical geographical location as a border outpost, Sirmione became a crucial defence and control garrison for the ruling nobles, retaining this function until the 16th century, when its role was taken up by Peschiera del Garda.