Marriage in France consist of one or two ceremonies. In any case there has to be a civil ceremny. The civil ceremony now is referred to as the Pacte civil de Solidarite or Pac. Originally the civil ceremony was intended only for heterosexual marriages. The PAC now includes same sex marriages and provides for most contingencies included in marriage vows concerning property and divorce. As a result many young, and not so young, people on both side of the sexual fence prefer the one step PAC and forget the religious ceremony.
In any case for a marriage to be recognized by the government there must be a civil ceremony. If you want a religious one as well, that is your choice. As the PAC simplifies the ins-and-outs of marriage, it has become a popular alternative.
I do not have wifi in the apartment and because the town hall does and the town hall for the 3rd district (arrondissement) is open Saturday mornings, I come in with my backpack with my laptop to one of the desks in the east or west wing to check my mail and read the papers. Before I pack up to leave I hear the crowd noises of guests coming to the town hall to watch a friend or friends get married that does not due justice to the red carpet on the elegant, late 19th C staircase to the first floor where the civil ceremonies are held.
Because the bride is wearing a traditional wedding gown, we assume that following the civil ceremony the couple and their friends will caravan to the church of their choice for for the religious ceremony followed usually by a formal and extensive luncheon with lots of liquid goodies.