One hundred years ago today, Forbes Field opened in Pittsburgh Pennsylvania. Credited as the first modern ballpark, the field was home to the Pittsburgh Pirates from 1909 until 1971. It also was the first home of the Pittsburgh Steelers, hosted University of Pittsburgh football games, and Negro League games. The stadium was named after British general John Forbes who fought in the French and Indian War, and named the city in 1758.
Built by Pirates owner Barney Dreyfuss, construction was completed in about 6 months at a cost of $1 million (roughly $24m in today's money). All that remains these days are the left and center field brick walls, the flagpole, and home plate (which is inside one of the buildings of Pitt). A ceremony is still held every year on October 13th by the remaining walls to commemorate Bill Mazeroski's Game 7, World Series clinching, bottom of the 9th walk-off home run (the only one in Major League history).
There are going to be some commemoration events on Tuesday, as well as a program at Pittsburgh's Senator John Heinz History Center (running through November 8th). There's a short video here that talks briefly about Forbes Field and the Heinz exhibit (I tried to embed it, but couldn't).