18th century, the Crimean Khanate maintained a massive slave trade with the Ottoman Empire and the Middle East which was one of the important factors of its economy. One of the most important trading ports and slave markets was Kefe. According to the Ottoman census of 1526, taxes on the sale and purchase of slaves accounted for 24% of the funds, levied in Ottoman Crimea for all activities. But in fact, there were always small raids committed by both Tatars and Cossacks, in both directions. The 17th century Ottoman writer and traveller Evliya Çelebi wrote that there were 920,000 Ukrainian slaves in the Crimea but only 187,000 free Muslims. However, the Ukrainian historian Sergey Gromenko considers this testimony of Çelebi a myth popular among ultranationalists, pointing out that today it is known from the writings on economics that in the 17th century, the Crimea could feed no more than 500 thousand people. For comparison, according to the notes of the Consul of France to Qırım Giray khan Baron Totta, a hundred years later, in 1767, there were 4 million people living in the Crimean khanate, and in 1778, that is, just eleven years later, all the Christians were evicted from its territory by the Russian authorities, which turned out to be about 30 thousand, mostly Armenians and Greeks, and there were no Ukrainians among them. Also, according to more reliable modern sources than Evliya's data, slaves never constituted a significant part of the Crimean population. Russian professor Glagolev writes that there were 1.800.000 free Crimean Tatars in the Crimean Khanate in 1666, it also should be mentioned that a huge part of Ukraine was part of the Crimean Khanate, that is why Ukrainians could have been taken into account in the general population of the Khanate by Evliya (see Khan Ukraine). Some researchers estimate that more than 2 million people were captured and enslaved during the time of the Crimean Khanate. Polish historian Bohdan Baranowski assumed that in the 17th century Polish–Lithuanian Commonwealth (present-day Poland, Ukraine and Belarus) lost an average of 20,000 yearly and as many as one million in all years combined from 1500 to 1644. In retaliation, the lands of Crimean Tatars were being raided by Zaporozhian Cossacks, armed Ukrainian horsemen, who defended the steppe frontier – Wild Fields – against Tatar slave raids and often attacked and plundered the lands of Ottoman Turks and Crimean Tatars.