Early engineers drew heavily for exemplars on the achievements of the past. Telford's employment as a county surveyor involved restoration of existing works. However, engineers were often accused of despoiling the existing environment; Telford himself was involved in the destruction of the precinct of St Katharine's by the Tower of London, and there are abundant examples of railways showing scant concern for the heritage through which they passed. In contrast, engineers like Benjamin Baker and Francis Fox used their engineering skills to extend the life of threatened structures. There is frequent debate between those seeking to improve the existing infrastructure and those who want such improvements to take account of the historic engineering heritage. Recent examples include the strengthening of Brunel's Thames tunnel and Network Rail's improvement works in Manchester. Heritage successes are often based on a few committed individuals using their engineering knowledge to mount successful campaigns. Despite more powerful analytical tools and ever-improving monitoring technology, structures like the internationally significant Union Suspension Bridge are under threat. Some may argue it all comes down to money, but is it in part a result of engineers' education and their lack of knowledge of their own heritage and sense of place?