 Complete the following phrase:  The opening was first analysed in depth in the 19th century, and received its name from the Berliners that examined its variations. Due to the defensive and drawish nature of the opening, it is sometimes referred to as the Berlin Wall. The opening was rarely used in high level games and received little attention until the Classical World Chess Championship 2000, in which challenger Vladimir Kramnik used it as a drawing weapon against champion Garry Kasparov. Kramnik used the Berlin in games 1, 3, 9 and 13 in the match each time as black, all four of which were drawn. After losing the match, Kasparov cited Kramniks superior opening preparation as a reason for his loss. In an interview with John Henderson, Kramnik described his use of the Berlin:The Berlin Defence suited my strategy for the match. I had a defensive strategy  Actually, I had in my pocket some other sharper stuff to fall back on  but first I wanted to try the defensive strategy with Black and it worked so well. This was all new to Kasparov  he probably expected me to fight for equality with Black.The 2000 match caused a resurgence of interest in the Berlin Defence at all levels of the game, such as its use by Magnus Carlsen and Viswanathan Ad in games 4, 6, 7 and 8 of the 