Sixth Edition, Classic
Sixth Edition, also known as Classic, was released on April 27, 1999. It contains 350 cards including both reprints of cards from previous core sets as well as new reprints from expansion sets through the Weatherlight expansion. The name "Classic" was prominently featured on cases of packs of the set, and the set was referred to by both titles by both Wizards of the Coast and players.
Sixth Edition was the first base set to have its artist information centered on the card (a printing practice started in Exodus). It was also the first base set to have collectors' numbers (which also originated in Exodus). The rules text on basic lands was also replaced with just a mana symbol, as featured in the Portal starter sets of 1997 and 1998.
Perhaps the biggest cosmetic change to the base set, however, was the expansion symbol. Sixth Edition was the first core set to have an expansion symbol, which was necessary to show the cards' rarities (another practice that originated in Exodus). The set's expansion symbol was the Roman numeral VI, or 6. (This change had occurred slightly earlier in the Traditional Chinese version of Fifth Edition, which used a Roman Numeral 'V' as the expansion set. The Traditional Chinese version came out notably later than the English version, by which time Wizards of the Coast had decided the feature was necessary.)