The church tower of All Hallows in the City of London is Grade 1 listed and is the only tower to survive the Great Fire and the Blitz. Over the centuries the surrounding ground level had risen and defective drainage meant that water was entering into the original massive Reigate stone columns. This had been exacerbated by hard cement render around the columns as well as a hard impervious floor which together encouraged moisture movement up the columns and significant damage to the masonry from salts. A proposal for redevelopment of the site involved lowering the ground level, moving an adjacent crypt and ensuring that the tower was conserved. In order to understand the complex issues involved, OCC were commissioned to carry out investigation and monitoring of the site. This involved regular inspection, environmental recording as well as time-lapse photography and salt analysis. Working closely with archaeologists from the Museum of London, the results have helped to inform the methodology to be used in protecting the tower during redevelopment and ensuring it has a sustainable future.