From University of Oldenburg (Germany)
http://www.bis.uni-oldenburg.de/bisverlag/spoall93/kap1.pdf
http://www.bis.uni-oldenburg.de/bisverlag/spoall93/kap1.pdf
Pope CALIXT III issued the decree on 29 June 1456 from cause of the loss of Morea to the Turks and for memory of the threat of Austria to ring in all churches at noon one or more bells against the Turks. All believers should pray at bell ringing 3 father ours and 3 ave maria. Isolated in some regions this bell ringing was present already in former times. Archbishop Wolfram of Prague had already ordered 1399 that each Friday at the hour of Christ's death the bell to be rung, in order to remeber the painful victory of the Turks over the Christians. Also in the case of Prague, humans had to stop all their activities and knee down to speak the prayer of the Lord five times.
How deeply this ringing entrenched itself in the consciousness of humans, also during a longer period of time, shows a lecture of the abbott Coelestin KOENIGSHOFER of the monastery of the Holy Cross, which still rang in 1797.
The abbott reported the fact that the bell ring was introduced first as to ask for God's assistance in the Turk danger and later than the ring belling was kept to thank for the rescue from the Turk danger.
Through several centuries the believers connected the Turk danger with the bell ring. The church, both the Evangelist and the catholic, reached with the daily combination of bell ring and prayer that each member of the municipality was reminded day for day of the Turk danger.