Many writers suppose that there is reference here to the Jewish custom of having proseuchae, or places of prayer, distinct from synagogues, and in locations where there were no synagogues. Though some commentators deny the reference to the custom in this passage, yet the existence of the custom itself is undeniable. The proseuchae were places for prayer outside of those towns where the Jews were too poor to have synagogues, or were not permitted to have them. They were generally located near the water for the convenience of ablution. Sometimes a large building was erected: but frequently the proseuchae was simply a retired place in the open air or in a grove.
Rivers seem to have been favorite places of resort for God’s people. In captivity they assembled “by the rivers of Babylon” (Psa. 137:11By the rivers of Babylon, there we sat down, yea, we wept, when we remembered Zion. (Psalm 137:1)). Ezekiel speaks of being among them “by the river of Chebar” (Ezek. 1:11Now it came to pass in the thirtieth year, in the fourth month, in the fifth day of the month, as I was among the captives by the river of Chebar, that the heavens were opened, and I saw visions of God. (Ezekiel 1:1)). Daniel was “by the river of Ulai” when he beheld one of his visions (Dan. 8:22And I saw in a vision; and it came to pass, when I saw, that I was at Shushan in the palace, which is in the province of Elam; and I saw in a vision, and I was by the river of Ulai. (Daniel 8:2)) and he saw another when he was “by the side of the great river, which is Hiddekel” (Dan. 10:44And in the four and twentieth day of the first month, as I was by the side of the great river, which is Hiddekel; (Daniel 10:4)). Dr. Pusey quotes from a decree of the Halicarnassians, which gave leave “that those of the Jews who willed, men and women. should keep the Sabbaths, and perform their rites according to the Jewish laws, and wake oratories by the sea according to their country’s wont” (Pusey on Daniel, pp. 110-111).