Ketubot 2 - Marriages are for Wednesdays
The custom was for people to get engaged, and then take a year to prepare for a wedding. This engagement had more legal power than today: they were husband and wife, except not living together. When the time came to marry, girls for whom it was the first marriage would get married on Wednesdays. Why specifically on this day? Because of another circumstance - the courts used to convene on Thursdays, so that if he had any question about his wife, he could come to court on the morrow. For example, if he had suspicions that she was unfaithful to him, judging by the fact that she was not a virgin, he could come to court, and expect that the publicity caused by his actions could bring in witnesses of her unfaithfulness, if such there were.
But why make a wedding on a Sunday, being that the courts convened on Mondays (and on Thursdays)? - Because then he would only have one day after Shabbat to prepare a wedding feast, and the Sages wanted the daughters of Israel to be respected with a celebration.
All the year of engagement the bride lives in her father's house. Once the year passes, the husband starts to supply her needs even if the marriage is delayed. The Talmud discusses this obligation of his under various unforeseen circumstances.
Art: Wedding Procession by Gustav Brion