Yermak's death, as his legend spread through the domain rapidly and, with it, the news of a land rich in furs and vulnerable to Russian influence. Colonization attempts soon followed, as Tyumen, the first known town after Yermak's death, was founded in 1586. The settling of this territory facilitated the establishment and development of Siberian agriculture. Most of these farmers were, in fact, soldiers, who grew their own sustenance out of necessity. Yermak had set a precedent of Cossack involvement in Siberian expansion, and the exploration and conquests of these men were responsible for many of the additions to the Russian empire in the east. After the initial return of the Cossacks shortly after Yermak's death, an ambitious project of fortification began under the direction of Boris Godunov. Its achievements, including the extension of protection for Russians in the region, would drive even greater numbers of entrepreneurs to Siberia. In 1590, Tobolsk received a significant boost in prominence as it was dubbed the principal city and administrative center of the region. The fur trade also continued to grow, aided by the Cossacks, who in 1593 established the trading center of Berezof on the Ob River at the sixty-fourth latitude. The practice of collecting tributes of fur from the natives continued to spread, and in the 17th century such furs made up 25–33 percent of the income to the tsar's treasury. Thus, as soon as fifteen years after Yermak's death, the basin of the Ob River had truly become a region of Russian influence. Even so, the Russians did not rest on their laurels, and the attitude and pace of expansion pioneered by Yermak continued well into the 17th century. Indeed, within the first half of the century the fort of Yeniseysk was established in 1619, the city of Yakutsk founded in 1632, and the important feat of reaching the Sea of Okhotsk on the Pacific coast in 1639. Throughout these campaigns, Yermak's influence was undeniable, as the pace he had established for achievement in his relatively short time in Siberia heralded a new age of Russian pioneering. Yermak's life and conquests had a significant impact on Russian policy towards Siberia and the colonization attempts that followed this shift. Prior to Yermak's agreement with the Strogonovs, the Russian attitude towards the Siberian expanse had been one preoccupied primarily with defense, not aggression. The top priority was the repelling of the Tatar