the bay from shore batteries. French forces reached as far as San Roque, just north of Gibraltar, but did not attempt to target Gibraltar itself as they believed that it was impregnable. The French besieged Tarifa, further down the coast, in 1811–12 but gave up after a month. Gibraltar faced no further military threat for a century. After peace returned, Gibraltar underwent major changes during the reformist governorship of General Sir George Don, who took up his position in 1814. The damage caused by the Great Siege had long since been repaired, but Gibraltar was still essentially a medieval town in its layout and narrow streets. A lack of proper drainage had been a major contributing factor in the epidemics that had frequently ravaged the fortress. Don implemented improved sanitation and drainage as well as introducing street lighting, rebuilding St Bernard's Hospital to serve the civilian population and initiating the construction of the Cathedral of the Holy Trinity to serve Gibraltar's Protestant civilians. For the first time, civilians began to have a say in the running of Gibraltar. An Exchange and Commercial Library was founded in 1817, with the Exchange Committee initially focused on furthering the interests of merchants based in the fortress. The Committee evolved into a local civilian voice in government, although it had no real powers. A City Council was established in 1821, and in 1830 Gibraltar became a Crown colony. In the same year, the Gibraltar Police Force was established, modelled on London's pioneering Metropolitan Police Service, and a Supreme Court was set up to try civil, criminal and mixed cases. The economic importance of Gibraltar changed following the invention of steamships; the first one to reach Gibraltar's harbour arrived there in 1823. The advent of steamships caused a major shift in trade patterns in the Mediterranean. Transshipment, which had previously been Gibraltar's principal economic mainstay, was largely replaced by the much less lucrative work of servicing visiting steamships through coaling, victualling and ferrying of goods. Although Gibraltar became a key coaling station where British steamships refuelled on the way to Alexandria or Cape Horn, the economic changes resulted in a prolonged depression that lasted until near the end of the century. The demand for labour for coaling was such that Gibraltar instituted the practice of relying on large numbers of imported Spanish workers. A shanty town sprang up on the site of the old Spanish