The chief business of the city has been carried on for many centuries in the Guildhall, which is of unknown antiquity. It is almost certain that the building was in existence on the same spot as early as the twelfth century. It was rebuilt in 1411, and has been greatly altered at different times since then. The most interesting portion of the old building will be found in the extensive Gothic crypt which is shown in the illustration on page 273. The open timber roof of the Hall was not added until the alterations of 1866-1870 by the late Sir Horace Jones. CHAPTER X _Commerce and Trade_ The earliest trade recorded as carried on in the British Isles consisted of the exchange of tin with the Gauls, and, perhaps, also with Phoenician traders. Under Roman rule the agricultural and mineral resources of Britain were more fully developed. Julius Cæsar praised the Southdown mutton, and Rome was supplied with oysters which came from Whitstable and Reculvers (_Regulbium_), and were carried through the River Stour (forming the western boundary of the Island of Thanet), and were exported from Richborough (_Rutupiæ_). Corn was exported in large quantities, and Londinium, the principal port for trading with Gaul, was the centre of commerce. There is no notice of commerce during the early Anglo-Saxon period, but Bede, at the beginning of the eighth century, speaks of London as a great market which traders frequented by land or sea. The letter of protection for English pilgrims given to Offa of Mercia by Charlemagne (A.D. 796), which refers to trade carried on by them, has been called 'the first English commercial treaty.' One remarkable fact is that this commerce was mainly in the hands of foreigners. London in the early times was mainly a city of foreigners. Hence the jealousy of the natives, which grew in strength as time went on. Commerce greatly increased during the reign of Edgar, so that Ethelred his son deemed it time to draw up a code of laws to regulate the Customs to be paid by the merchants of France and Flanders, as well as by the Emperor's men, but the promulgation of the laws of Athelstane (A.D. 925-929), which ordained that a merchant who had made three sea voyages should be of right a Thane, is a proof of the small number as well as of the importance of such native traders. We learn from the Colloquies of the Abbot Ælfric (eleventh century) that most of the commodities imported into England were articles of luxury. The port of Dowgate was granted to the City of Rouen as early as Edward the Confessor's reign, and the right was afterwards confirmed.[285] The Confessor also gave a portion of Waremanni-Acra within London, 'with the wharf belonging to it, and with its market rights and places for merchandise, its stalls and shops, its rents and dues and rights, its toll and wharfage' to St. Peter's at Ghent, which grant was confirmed by William I. 1081.[286]