by the natives. Early in the period, Hallstatt slashing swords and daggers were a significant import, but by the mid-6th century, the volume of goods arriving seems to have declined, possibly from more profitable trade centres appearing in the Mediterranean. La Tène culture items (usually associated with the Celts) appeared in later centuries, and again, they were adopted and adapted with alacrity by the locals. There also appears to have been a collapse in the bronze trade during the early Iron Age, which can be viewed in three ways: Steady transition: the development of iron parallel to a diminishing bronze system. Rapid abandonment; iron undermines bronze and takes over its social function. Bronze crisis: severe reduction in the supply of bronze allows the iron to replace it. With regard to animal husbandry, cattle represented a significant investment in pre-Roman Britain, as they could be used as a source of portable wealth and to provide useful domestic by-products such as milk, cheese and leather. In the later Iron Age, an apparent shift is visible, revealing a change in dominance from cattle rearing to that of sheep. Economically, sheep are significantly less labour-intensive, requiring fewer people per animal. Cattle and sheep dominate the osteo-archaeological record, but evidence for pig, ox, dog and rarely chicken is widely represented. There is generally an absence from environmental remains of hunted game and wild species as well as fresh and sea water species, even in coastal communities. A key commodity of the Iron Age was salt, used for preservation and the supplementation of diet. Though difficult to find archaeologically, some evidence exists. Salterns, in which sea water was boiled to produce salt, are prevalent in the East Anglia fenlands. Additionally, Morris notes that some salt trading networks spanned over 75 km. Representing an important political and economic medium, the vast number of Iron Age coins found in Great Britain are of great archaeological value. Some, such as gold staters, were imported from Continental Europe. Others, such as the cast bronze (potin) coins of Southeast England, are clearly influenced by Roman originals. The British tribal kings also adopted the continental habit of putting their names on the coins they had minted, with such examples as Tasciovanus from Verulamium and Cunobelinos from Camulodunum identifying regional differentiation. Hoards of Iron Age coins include the Silsden Hoard in West Yorkshire found in 1998. A large collection of coins, known as