Ljubljana's Roman ruins are the surviving fragments of Emona, the walled settlement that stood here long before the Habsburg façades and riverside cafés. Walls, gates, early Christian remains, and archaeological displays are scattered around the southwest side of the centre rather than concentrated in one grand ruin.
They are most rewarding if you treat them as a city walk. Follow the traces near Mirje and the City Museum, and the modern street plan starts to feel layered rather than merely pretty.