There were two principal forms of marriage ceremony observed in Ancient Rome. There was the more formal, legally binding ceremony observed by the upper classes, or Citizens of Rome, and there was the less formal ceremony which appled to non-Citizens.
In the case of the former, engagements or betrothals were commonplace but neither essential nor in any way binding. The giving of a ring symbolised the event and - like the future wedding ring - would be worn on the third finger of the left hand, as it was the belief at the time that a vein led from here straight to the heart.
On the morning of her wedding, the bride to be was traditionally dressed by her mother, her tunic tied in a symbolic knot which only her new husband could later untie. The wedding ceremonies themselves were usually held at the home of the bride's father, who would have been expected to have paid a dowry to his new son-in-law. The ceremony would take the form of the couple holding hands and exchanging their vows in the presence of at least ten witnesses, representing the ancient ten tribes of the people. A feast was commonly held thereafter before the husband would lead his bride in a formal procession to his own home, symbolising his taking her away from her father as his own new property. There was no such thing as divorce in Ancient Rome but following her marriage a woman's status was greatly enhanced and she became very much the mistress of her new household.
There is no known ceremony which took place in the case of marriages between non-Citizens. It is believed that it essentially involved only a man and a woman from the lower class setting up home together and living as though man and wife. If the couple later became Citizens of Rome, their marriage was generally legalised, though no one-time non-Citizen could ever marry a lifetime Citizen.
There is one other extremely significant fact regarding marriage in Ancient Rome worthy of mention. In the 3rd Century AD, the Emperor Claudius II was having significant trouble persuading men to leave their wives and families to join his army. He therefore took the somewhat drastic step of annuling all existing marriages and banning any future ones. Sympathetic to the plight of many young lovers, a priest by the name of Valentine continued to marry them in secret until he was discovered and sentenced to death. While awaiting execution, the young daughter of one of his guards befriended him and when he was taken away to be beaten to death on February 14th 269 AD, he left her a thank you note signed, "Love from your Valentine..."