Arrhae Ceremony

Sometime after the exchange of vows, the groom presents the arrhae or arras to his bride after it has been blessed by the priest.

The arras, Spanish for "earnest money", is said to come from a Roman custom of breaking gold or silver into equal halves by both parties as a pledge of marriage.

The thirteen coins, said to represent Christ and his 12 apostles, symbolize the groom's unquestionable trust and confidence. By giving arras to his bride, he places all his material wealth into her care. Acceptance by the bride means taking that trust unconditionally with total dedication.

It is also said that the custom came from Spain. The arras usually come in ornate boxes or gift trays and represents the bride's dowry as well as good wishes for prosperity. Oftentimes, these coins become part of the family heirloom.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Source:
Mexican Wedding Traditions. The Thirteen Gold Coins.
http://www.weddingdetails.com/lore/mexican_content.cfm#traditions/