This example recreates Charles Minard’s classic 1812 Napoleon march chart, tracing army size against longitude for both the advance to Moscow and the retreat, with a temperature annotation at the coldest point. The D3.js v7 code uses `scaleLinear` for axes, `scaleOrdinal` for the advance/retreat color encoding, and `curveCatmullRom` line smoothing. A React wrapper in `app.jsx` uses a `ResizeObserver` to feed container dimensions into the D3 rendering pipeline, which builds axes, legend, and the line-and-circle marks. The data is loaded from a CSV via `d3.csv`.