Most datacenter network (DCN) designs focus on maximizing bisection bandwidth rather than minimizing server-to-server latency. We explore architectural approaches to building low-latency DCNs and introduce Quartz, a design element consisting of a full mesh of switches. Quartz can be used to replace portions of either a hierarchical network or a random network. Our analysis shows that replacing high port-count core switches with Quartz can significantly reduce switching delays, and replacing groups of top-of-rack and aggregation switches with Quartz can significantly reduce congestion-related delays from cross-traffic. We overcome the complexity of wiring a complete mesh using low-cost optical multiplexers that enable us to efficiently implement a logical mesh as a physical ring. We evaluate our performance using both simulations and a small working prototype. Our evaluation results confirm our analysis, and demonstrate that it is possible to build low-latency DCNs using inexpensive commodity elements without significant concessions to cost, scalability, or wiring complexity.