After the peace treaty at the end of the
Second Northern War in 1660,
Frederick III of Denmark-Norway commissioned Ruse to reconstruct the damaged fortifications of
Copenhagen. In 1661, he was appointed quartermaster general, chief inspector of fortifications and colonel of an infantry regiment. Ruse immediately submitted a plan for rebuilding the
Copenhagen citadel which was accepted. Construction work, completed three years later, caused some bitterness among the local citizens, leading as far as threats to Ruse's life. In 1667, Ruse also completed the defences of Frederiksort in the
Duchy of Schleswig. He travelled around Denmark, inspecting and repairing the defences, especially those in
Kronborg,
Nyborg and
Fredericia. Thereafter he was involved in large-scale civil construction work in Copenhagen including cemeteries and monuments including the one to
Corfitz Ulfeldt. But above all, he drew up plans for two new districts, one to the northeast of
Kongens Nytorv and Gothersgade (Frederiksstaden) which included the
Nyhavn Canal, the other southwest of
Slotsholmen (Frederiksholm). In 1664, Ruse was appointed major general and member of the war cabinet. With the threat of war with England, he was sent to
Norway together with
Frederik Ahlefeldt in 1667. In 1669, he became commander of
Fredericia and, in 1671, commander in chief responsible for fortifications in the duchies. From 1667 to 1670, he also coordinated significant extensions to the Copenhagen and
Christianshavn ramparts. He had hoped to undertake a much more extensive project on both sides of the
River Eider but this was hampered by resistance from Hans von Schack, an influential military expert. At the beginning of
Christian V's reign, he rebuilt the entrenchments on a small island in the
River Elbe and completed a comprehensive report on the fortification system for the Danish-Norwegian monarchy. ==Titles and property==