it would be crushed, then washed. The less dense rock would wash away, leaving behind the iron oxide, which would then be smelted using the bloomery method. The iron was heated up to 1500 °C using charcoal. The remaining slag was removed and generally dumped. After being smelted, the iron was sent to forges, where it was reheated, and formed into weapons or other useful items. Roman iron was thought to hold more value than other metals due to the tedious production through direct or bloomery smelting. A recovered Vindolanda tablet documents the purchase of 90 Roman pounds of iron for 32 denarii by a man named Ascanius. This amounted to 1.1 denarii per kilogram of iron. Coal For both domestic and industrial use, coal provided a considerable proportion of the fuel required for warmth, metal-working (coal was not suitable for the smelting of iron, but was more efficient than charcoal at the forging stage) and the production of bricks, tiles and pottery. This is demonstrated by archaeological evidence from sites as far apart as Bath, Somerset (the temple of Sulis and household hypocausts), military encampments along Hadrian's wall (where outcrop coal was worked near the outlying fortlet at Moresby), forts of the Antonine Wall, Carmel lead mines in north Wales and tile kilns at Holt, Clwyd. Excavations at the inland port of Heronbridge on the River Dee show that there was an established distribution network in place. Coal from the East Midlands coalfields was carried along the Car Dyke for use in forges to the north of Duroliponte (Cambridge) and for drying grain from this rich cereal-growing region. Extraction was not limited to open-cast exploitation of outcrops near the surface: shafts were dug and coal was hewn from horizontal galleries following the coal seams. Working conditions Some miners may have been slaves, but skilled artisans were needed for building aqueducts and leats as well as the machinery needed to dewater mines and to crush and separate the ore from barren rock. Reverse overshot water-wheels were used to lift water, and sequences of such wheels have been found in the Spanish mines. A large section of a wheel from Rio Tinto can be seen in the British Museum, and a smaller fragment of a wheel found at Dolaucothi shows they used similar methods in Britain. The working conditions were poor, especially when using fire-setting under ground, an ancient mining method