The Gemara relates the well-known story of Nakdimon ben Guryon, who is known from a number of stories that appear about him in the Talmud as one of the wealthy Jews who lived in Jerusalem at the time of the destruction of the Second Temple. (There appear to be references to him in Josephus’ works, as well.) While his Hebrew name was Buni – as is mentioned in the Gemara – it was common for members of the upper class to have Roman names, as well. His Roman name – Nakdimon – is the subject of a Rabbinic midrash, as is related in the story told by the Gemara.
One year, during a drought, there was no water available for the Jewish pilgrims who were coming to Jerusalem for the holiday. Nakdimon ben Guryon approached one of the Roman officers with an offer. He wanted access granted to twelve Roman cisterns on behalf of the Jewish pilgrims. He personally guaranteed that the cisterns would be refilled by a certain date, or else he would pay him twelve talents of silver. When the day arrived, the Roman officer demanded to receive either the water or the silver. Nakdimon ben Guryon responded that the day was not yet over. The officer ridiculed the notion of Nakdimon ben Guryon expecting the cisterns to be refilled in a year of drought. Laughing, he went to the bathhouse, looking forward to his windfall. Nakdimon went to the Temple and prayed to God that his concern for the Jewish people should not lead to financial ruin. The skies filled with clouds and rain began to fall, filling the cisterns. Upon completing their missions, Nakdimon and the Roman officer met outside in the rain. Nakdimon pointed out that the cisterns were not only filled, but were overflowing, and he claimed that the Roman owed him the overflow. The Roman admitted that God had brought the rain on behalf of Nakdimon, but he argued that the debt had not been paid on time, for the day was over! At this point, Nakdimon prayed and the clouds dispersed, allowing the sun to break through – nikdera hamah ba’avuro – proving that the day was not over. (And hence the name Nakdimon.)
On a literary note, the Maharsha points out the contrast in the story, of the Roman officer entering the bathhouse – the beit hamerhatz – to bathe while people are desperate for water, whereas Nakdimon exits the Beit HaMikdash and demands that the excess water be made available to the people.