On the plaza before the Memorial Church there is this fountain called "verbum dei manet in aeternum", what translates from Latin as "The word of God stays in eternity". This bible word was the motto of the princes and the imperial free cities at the general assemby in Speyer in 1529, which became to be known as the protestation of Speyer, and which is the event that the memorial church is reminding of.
Unfortunately this fountain is dry for years now, and therfore is overseen frequently.