One correct answer
Now turn around and look! There's the famous Narva river! Lots of folks came to Narva by sea and continued their travelling on the waves of Narva river. From the river, they sailed forward to the East to St Petersburg or to the South to Peipsi lake and from there on to Pihkva or Tartu! But many also came by land and their post chariots were often stopped and checked before entering the city. Why was that so?