There is some debate about where this custom originated, some site Spain, but it's a traditional in Latin and Filipino weddings!
The madrina de arras holds the 13 coins the bridegroom presents to the bride. The coins, or arrhea, was a Roman custom of breaking gold or silver, one half to be kept by the woman and the other half by the man, as a pledge of marriage.
The groom gives the bride thirteen gold coins as a symbol of his unquestionable trust and confidence. He pledges that he places all of his goods into her care and safekeeping. Acceptance by the bride means taking that trust and confidence unconditionally with total dedication and prudence.

The custom of the coins originated in Spain. Thirteen coins are given to the bride by the bridegroom, signifying he will support her. Often presented in ornate boxes or gift trays, this represents the brides dowry and holds good wishes for prosperity. These coins become a part of their family heirloom.

The number 12 represents Christ and his 12 apostles. The coins are presented to the priest by a friend or relative (usually the purchaser). The priest then blesses the coins and hands them to the bride who places them in the groom's cupped hands at the beginning of the ceremony. The coins are then placed on a tray and handed to an assistant to be held until later in the ceremony. Near the end of the ceremony the box and coins are given to the priest who places the coins in the box and hands them to the groom.

The groom will then pour the coins into the bride's cupped hands and places the box on top. This represent his giving her control as his mistress of all his worldly goods. (Sometimes their hands are tied with a ribbon for this portion of the ceremony.)

Image & Article Via: Wedding Details

 
Top