 The cause of this debt was Hamburg's contribution to the Schmalkaldic War (1546–1552) between the Lutheran dukes and cities and the emperor.When the Senate commissioned Jan van Valckenborgh to build a second layer to the city's fortifications to protect against the Thirty Years War (1618–1648), Hamburg was also extended by the newly created "New Town" ("Neustadt").Some of these street names still date from the grid system of roads he introduced.