A Commonwealth army under the command of Hetman Stanisław Żółkiewski, who was generally opposed to this conflict but could not disobey king's orders, crossed the border and on 29 September 1609 laid siege to Smolensk, an important city Russia had captured from Lithuania in 1514. Smolensk was manned by fewer than 1,000 Russian men commanded by the voivod Mikhail Shein, while Żółkiewski commanded 12,000 troops. However, Smolensk had one major advantage: the previous Tsar, Boris Godunov, had sponsored the fortification of the city with a massive fortress completed in 1602. The Poles found it impenetrable; they settled into a long siege, firing artillery into the city, attempting to tunnel under the moat, and building earthen ramparts, remnants of which can still be seen today. The siege lasted 20 months before the Poles advised by the runaway traitor succeeded in taking the fortress.