Behind his museum Schinkel himself had built in 1828-32, along the banks of the Kupfergraben, the Packhofgebäude. This range of utilitarian structures was definitely consonant, towards the Museum, with the Grecian rationalism of its rear façade. But for the warehouses at the remote end of the group Schinkel used a rather direct transcription of Durand’s paradigm for an arcuated market.[48] Here, at almost precisely the same time as at Gärtner’s State Library in Munich and Hübsch’s Ministry of Finance in Karlsruhe, the _Rundbogenstil_ makes an early appearance as an alternative to the trabeated Grecian. In comparably utilitarian works of a few years earlier, the Military Prison in Berlin begun in 1825 and the lighthouse at Arkona of the same date, Schinkel had already used dark brickwork unstuccoed, but with square rather than arched openings; while on his long-demolished Hamburg Opera House, begun also in 1825 and completed in 1827, there were arched openings throughout of a somewhat High Renaissance order but far more severely treated than by Klenze on his Munich Pinakothek. To the year 1825 belongs too the beginning of the Werder Church in Berlin, Gothic in its vaults, as also in its detail, and executed in brick and terracotta. Less just in its scaling than his earlier Gothic monument of cast iron, this church as executed makes one regret that Schinkel’s domed project of 1822, derived either from Vignon’s interior of the Madeleine in Paris or from one of Durand’s paradigms, was not executed. In 1826 began Schinkel’s extensive and varied work for the Royal family at Potsdam,[49] the town destined to be the richest centre of later Prussian Romantic Classicism. Here he worked in close association with the heir to the throne who was later, after 1840, king as Frederick William IV. This romantic and talented prince—who actually wished he were an architect rather than a ruler—frequently provided Schinkel and, after his death, Schinkel’s pupils with sketches from which as we have seen in the case of the Nationalgalerie) various executed buildings were elaborated with more or less success. One of the great amateurs, his was a very late example of direct Royal intervention in architecture. Some of the modulation of Schinkel’s style towards the Picturesque—still more evident in the work at Potsdam of his ablest pupil Ludwig Persius (1803-45)—may be credited to this princely patron.