Tunnel of Boston’s MBTA blue line.

Earliest tunnels were home improvement projects; cave dwellers appear to have thus enlarged their living quarters. But the ancient Babylonians may have been among the first to use tunnels for irrigation, in addition to building a passage from palace to temple under the Euphrates River. Tunnels have advantages beyond their ability to connect distant points. Environmentally, there are benefits to placing transportation underground where emissions can be more easily captured and treated. If tunnels are re-imagined as tubes, floating throughways may one day transit straits and even oceans.

Building the World Blog by Kathleen Lusk Brooke and Zoe G Quinn is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.