In the Chiefs' first two seasons attendance did not match the levels Mayor Bartle had promised, but in 1966 average home attendance at Chiefs games increased and reached 37,000. By 1969 Chiefs' average home attendance had reached 51,000. In 1966 the Chiefs won their first AFL Championship (after having previously won it as the Dallas Texans) and reached the first-ever Super Bowl, which the Chiefs lost to the Green Bay Packers. The Chiefs remained successful through the 1960s, and in 1970 the Chiefs won the AFL Championship and Super Bowl IV (the last Super Bowl played when the AFL was a separate league prior to it being absorbed into the NFL as the American Football Conference) over the heavily favored Minnesota Vikings.