Russians under Field Marshal Joseph Vladimirovich Gourko succeeded in capturing the passes at the Stara Planina mountain, which were crucial for maneuvering. Next, both sides fought a series of battles for Shipka Pass. Gourko made several attacks on the Pass and eventually secured it. Ottoman troops spent much effort to recapture this important route, to use it to reinforce Osman Pasha in Pleven, but failed. Eventually Gourko led a final offensive that crushed the Ottomans around Shipka Pass. The Ottoman offensive against Shipka Pass is considered one of the major mistakes of the war, as other passes were virtually unguarded. At this time a huge number of Ottoman troops stayed fortified along the Black Sea coast and engaged in very few operations.