Which is the more durable. The painted steel of the Maria Valeria bridge or the chestnut tree standing sentry beside it? The latest bridge is celebrating its tenth anniversary this year, whilst  the tree according to local knowledge is at least fifty. The natural state of iron is oxide wrote the respected Victorian writer John Ruskin and without a coat of this pale utilitatian green every four or five years it will be well rusted in another ten. The seemingly more frail tree, loses its leaves every autumn, but is less susceptible to the insessant weathering and its sticky buds are already set for its own springtime greening.