Following his triumph, Napoleon imposed the first elements of the Continental System through the Berlin Decree issued in November 1806. The Continental System, which prohibited European nations from trading with Britain, was widely violated throughout his reign. In the next few months, Napoleon marched against the advancing Russian armies through Poland and was involved in the bloody stalemate at the Battle of Eylau in February 1807. After a period of rest and consolidation on both sides, the war restarted in June with an initial struggle at Heilsberg that proved indecisive.