What election-law change did Gaius Marius propose as tribune of the plebs?

As tribune of the plebs in 119 BCE, Gaius Marius proposed a bill to reform election procedures by narrowing the "bridges"—the narrow gangways voters crossed to deposit their ballot tablets.1

By narrowing these passages, Marius ensured there was no longer enough room for observers, typically aristocrats, to stand alongside the voters. This change was designed to prevent those observers from intimidating or influencing an individual's vote. When the consuls attempted to have the Senate block this measure, Marius threatened them with imprisonment, and the bill was successfully passed.1