 Complete the following phrase:  In order to repel future PolishLithuanian attacks, Boris Godunov made it his priority to heavily fortify the city. The stone kremlin constructed in 15971602 is the largest in Russia. It features thick walls and numerous watchtowers. Heavy fortifications did not prevent the fortress from being taken by the PolishLithuanian Commonwealth in 1611 after a long twenty-month siege, during the Time of Troubles and 