Mamonovo (Russian: Мамоново, German: Heiligenbeil,[7] Polish: Święta Siekierka[2] or Świętomiejsce, Lithuanian: Šventapilė)[8] is a town in Kaliningrad Oblast, Russia, near the border with Poland.

[2] It was later renamed Heiligenbeil after a holy axe used by Augustinian monks, established in the area by Grand Master Winrich von Kniprode after the Battle of Rudau, to cut down an oak tree worshiped by pagan Prussians.

[15] Towards the end of the war in fierce fighting between January and March 1945 the Heiligenbeil pocket fell to the Red Army.

The defending 4th Army's archives were buried in a forest near the town and found in 2004, in an area still littered with debris from the final battles.

[1] As a municipal division, the town of oblast significance of Mamonovo is incorporated as Mamonovsky Urban Okrug.