Netherlands Bach Society informs us:
There was great excitement in Weimar, when Prince Johann Ernst returned in 1713 from the Netherlands, where he spent a great deal of money getting lots of music copied and bound, including a collection of music by Benedetto Marcello. Bach arranged the string concerto no. 2 from this collection for keyboard, which he probably created to liven up the dinners at the Saxe-Weimar home.
Says the harpsichordist, “I think Bach really liked the Italian concerti, because that was the new fashion also of the period.”