In 1880, 632 years after its foundations were laid, Cologne Cathedral was considered finished. This seems like an unquestionable fact: the dates are recorded in historical records – the progress and story well documented. It’s tempting to take this all as read and use the word ‘finished’ to confirm a linear timeline: the cathedral was started, it was built and eventually completed. But what if we stepped outside this chronology of events and the concept of ‘completion’ altogether? To consider this, we must remember that each piece added over the hundreds of years didn’t enter a fixed, unchanging state when installed, and thus would inevitably suffer the weathering that occurs on exposure to the elements. Each section of the cathedral is on a different material ‘timer’ with some being hundreds of years older than others – so the extent of these changes brought on by time and weather vary immensely. The desired effect of a ‘whole’ building, consistent in style and appearance, in this case could have only been reached through constant preservation alongside addition. As some pieces were added, others began to decay and crumble. Cologne is exceptional in its timespan, but in a more general sense, there is a blurred line that emerges in buildings – cathedrals being a good example – that have taken a significant time to ‘build’ and arguably are still undergoing this. When does building stop and conservation start?