 In fact, according to the terms of the Treaty of Wehlau and Bromberg, the House of Hohenzollern's sovereignty over the Duchy of Prussia was not absolute but contingent on the continuation of the male line (in the absence of which the duchy would revert to the Polish crown).Therefore, out of deference to the region's historic ties to the Polish crown, Frederick made the symbolic concession of calling himself "King in Prussia" instead of "King of Prussia".His royalty was, in any case, limited to Prussia and did not reduce the rights of the Emperor in the portions of his domains that were still part of the Holy Roman Empire.