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His death, which happened in his berth,
At forty-odd befell:
They went and told the sexton, and
The sexton tolled the bell.
Faithless Sally Brown -- Thomas Hood
Although I am no longer a Roman Catholic, the antiquity and the intricacy of Latin Catholic customs continue to intrigue me, and there are few things as incredibly solemn as a celebration of the Tridentine Mass, incense, candles and all (ok, so I was once an altar boy, sue me).
Bells are an essential part of the Latin liturgy, both the large ones that sit on church towers, and the small tintinnabulum bells rung at the Mass during elevations of the sacred Host.
The large bells had many uses throughout history. Since the church was often the centre of a small town, it would be used for marking such times as the beginning of the curfew, the ending of wars, new baptisms, and marriages. Many bells in Catholic churches have inscriptions, such as these taken from the Catholic Encyclopaedia:
Laudo Deum verum plebem voco congrego clerum
Defunctos ploro, nimbum fugo, festa decoro.
(I praise the true God, I call the people, I assemble the clergy;
I bewail the dead, I dispense storm clouds, I do honour to feasts.)
And:
Funera plango fulmina frango sabbata pango
Excito lentos dissipo ventos paco cruentos
(At obsequies I mourn, the thunderbolts I scatter, I ring in the sabbaths;
I hustle the sluggards, I drive away storms, I proclaim peace after bloodshed.)
The large church bells are also involved in a devotion known as the Angelus. This is a custom from the late middle ages, where a prayer is said in time to the ringing of the bells three times a day (6am, noon, and 6pm). Officially, a plenary indulgence is granted to those who perform this devotion a hundred days in a row, on their knees, except during saturday and sunday. I think this has changed since Vatican II (the last congregation of bishops at Rome to determine theology).
The bell is rung on every line of the prayer, which comes from the Alma Redemptoris (I think), a devotional antiphon to Mary.
Ding!
Angelus Domini nuncavit Mariae (The angel of the Lord declared unto Mary)
Ding!
Et concepit de Spritu Sancto (And she conceived of the Holy Spirit)
Ding!
Ave Maria gratia plena... (Hail Mary, full of grace...)
You get the idea.
The large bells are also rung (not in all places) at the major elevation of the Host during Mass, when the priest says "Hoc est corpus meum" (This is my body). The notion is that so people outside can kneel during the elevation to adore the body of Christ. I learned when I was an altar boy that this was not done in Masses said by the Pope or by cardinals.
Aside from this the small bells, the tintinnabulum were also rung at specific times during Mass. Four times in the reformed Vatican II Mass, and many more in the Tridentine mass.
In the past, only acolytes and ushers, which were minor clerical orders, were allowed to ring the bell. Since Vatican II, the minor orders have been supressed, so now, anyone rings them. Canon Law prohobits their use for non-religious purposes. | 
