On average, wireless electronics devices are replaced every 50 months. On average, a bridge is replaced every 50 years. As we begin to imagine integrating electronics and intelligence into the built environment, we need to to begin to think about electronic devices and systems on infrastructure timelines. This is not to say that every individual electronic device can, will, or should last for decades, but much like the ship of Theseus, the system that defines emerging Smart Cities will have a lifetime reaching into the century-scale. In this paper, we contemplate what the devices, gateways, network architectures, and their management might look like for a system designed to operate for decades. The result is a mixture of actionable insights for today and research questions for tomorrow, which culminates in the commencement of a 50-year experiment designed to see how long energyharvesting sensors, without the implicit lifetime of batteries, can remain viable without human attention or intervention.