The main entrance to the church is named the Giant's Door, or "Riesentor", possibly referring to the thighbone of a mammoth that hung over it for decades after being unearthed in 1443 while digging the foundations for the north tower, or else to the funnel shape of the door, from the Middle High German word "risen", meaning 'sink or 'fall'. The tympanum above the Giant's Door depicts Christ Pantocrator flanked by two winged angels, while on the left and right are the two Roman Towers, or "Heidentürme", that each stand at approximately tall. The name for the towers derives from the fact that they were constructed from the rubble of old structures built by the Romans (German "Heiden" meaning heathens or pagans) during their occupation of the area. Square at the base and octagonal above the roofline, the "Heidentürme" originally housed bells; those in the south tower were lost during World War II, but the north tower remains an operational bell tower. The Roman Towers, together with the Giant's Door, are the oldest parts of the church.