An air raid water reservoir, used for fighting fire during the war, was built in the middle of Hradčanské Square in 1944. This site is well documented thanks to archeological excavations carried out by the castle archeologist Ivan Borkovský, who made an important discovery while excavating the reservoir. He found the first Romanesque building constructed in the area west from the gates of today's castle, on the site of the former town of Hradčany. A one-room house made of ashlar masonry from the 12th–13th centuries was found in the place of the reservoir in its whole ground plan up to the height of 4 rows of ashlars. In this form it was transferred beneath Prague Castle, below the third courtyard, where it is found today, presented in its authentic form.The finding was published in 1988 by Jan Frolík, Archeologický výzkum na Hradčanském náměstí v r. 1944 / Archaeological excavations at Hradčanské náměstí (Hradčany square) in 1944. Castrum Pragense I, Praha, 1988, pp. 137–175. A second similar building was recorded by archeologists at Hradčany as recently as 2009, under the nearby pavement in front of Salmovský Palace.The discovery is documented in the archeological exhibition in Salmovský Palace (National Gallery in Prague).

While taking the picture of the reservoir, Sudek pointed his camera towards Salmovský Palace (no. 186/IV) on the southern side of the square. On the far right he captured a fragment of Schwarzenberg Palace (no. 185/IV), where the so-called Heeresmuseum Prag (Army Museum) was located in 1941–1945, its collections were mostly based on confiscations. However, the museum was never open to the public. There were also apartments for the employees of the office of the Reich's protector.Jiří Padevět, Průvodce protektorátní Prahou. Místa – události – lidé, Academia, Praha, 2013, p. 14.