Caesar crosses the Rubicon

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Caesar leads a legion out of his province into Italy, beginning civil war. The traditional date of 10 January 49 BCE is calculated in the unreformed pre-Julian calendar and is not securely convertible. The structural fact matters more than the date: a professional army had become loyal to its paymaster-general rather than to the Senate, and no republican institution could countermand it.

A node is not a place. Drawing it on a map would assert something about the world that no stored fact supports.