CINCINNATI -- Consider Cincinnati today Ground Zero in the debate over gay marriage.

A federal appellate panel this afternoon is hearing arguments from lawyers representing four states – Ohio, Kentucky, Michigan and Tennessee – as they defend their bans on same-sex marriage.

It marks the broadest attack yet on states' rights to define marriage as between a man and a woman.

READ FULL Enquirer ARTICLE : Gay marriage bans in 4 states go before court

The hearing on the courthouse's fifth floor is set to be a three-hour marathon of arguments from each state, beginning with Michigan, then followed by Ohio, Kentucky and Tennessee.

The states so far have waged their battles separately to uphold the bans that voters years ago embraced. So far, the states have lost: Federal judges in each have ruled against the bans, and the states have appealed, landing the cases in the appellate court.

Among the four states, Kentucky stands out because Attorney General Jack Conway refused to defend his state's ban, saying that doing so would require him to defend discrimination. Gov. Steve Beshear – like Conway, a Democrat – hired outside counsel to handle the case for the state. The other three states will be represented by their attorneys general.

REALTED : Court of Appeals to hear arguments in 6 marriage cases