It may be the oldest standing structure in Chicago: a cracked, pockmarked limestone obelisk, about four feet high, standing atop an equally cracked, pockmarked pediment at the south end of Calumet Park. Erected in 1838, it marks the border between two neighbors who don’t have much in common, and haven’t always been neighborly: Illinois and Indiana. Right behind it is a triumphal stone arch marking the entrance to a Northern Indiana Public Service Company power station. It’s the gateway to Indiana. Hoosiers are not renowned for their monuments – they’d rather show off a covered bridge – but this arch looks like a monument to the rivalry between two states, an attempt to awe Chicagoans who step across the border.