Club Martus was a casino bar located on Deep Space 9's Promenade opposite Quark's. It was opened and owned by an El-Aurian named Martus Mazur in 2370 and contained numerous gambling devices.
The popularity of Mazur's casino drew many customers away from Quark's. A run of bad luck, however, forced Mazur to close the casino only a few days after opening. (DS9: "Rivals")