Article: Vladimir had been prince of Novgorod when his father Sviatoslav I died in 972. He was forced to flee to Scandinavia in 976 after his half-brother Yaropolk had murdered his other brother Oleg and taken control of Rus. In Scandinavia, with the help of his relative Earl Håkon Sigurdsson, ruler of Norway, Vladimir assembled a Viking army and reconquered Novgorod and Kiev from Yaropolk. As Prince of Kiev, Vladimir's most notable achievement was the Christianization of Kievan Rus', a process that began in 988. The Primary Chronicle states that when Vladimir had decided to accept a new faith instead of the traditional idol-worship (paganism) of the Slavs, he sent out some of his most valued advisors and warriors as emissaries to different parts of Europe. They visited the Christians of the Latin Rite, the Jews, and the Muslims before finally arriving in Constantinople. They rejected Islam because, among other things, it prohibited the consumption of alcohol, and Judaism because the god of the Jews had permitted his chosen people to be deprived of their country. They found the ceremonies in the Roman church to be dull. But at Constantinople, they were so astounded by the beauty of the cathedral of Hagia Sophia and the liturgical service held there that they made up their minds there and then about the faith they would like to follow. Upon their arrival home, they convinced Vladimir that the faith of the Byzantine Rite was the best choice of all, upon which Vladimir made a journey to Constantinople and arranged to marry Princess Anna, the sister of Byzantine emperor Basil II.

Now answer this question: When did the Christianization of Kievan begin?
988