The Ariel Square Four is one of the most distinctive and technically fascinating British motorcycles ever built. Conceived in 1928 by Edward Turner—who would later become one of the most influential figures in motorcycle design—the Square Four was unlike anything else on the road. Its unique four-cylinder, four-stroke engine featured a compact "square" layout, with two parallel twin-cylinder blocks arranged in tandem, sharing a single crankcase. This design allowed for a powerful yet remarkably smooth-running engine, setting it apart from the singles and twins that dominated the era.

By the time the final iteration, the 4G Mk II, was introduced in 1953, Ariel had refined the Square Four into a 997cc powerhouse. With an alloy cylinder head, improved cooling, and a distinctive twin-pipe exhaust, the Mk II delivered effortless performance and an unmistakable sound. Despite its luxury status and impressive engineering, production ended in 1959, making the surviving Square Fours highly sought after by collectors and enthusiasts alike.

Today, the Square Four remains an icon of classic British motorcycling—an elegant grand tourer with a reputation for refinement, smooth power delivery, and an undeniably unique presence. Finding an original example, let alone one with a freshly rebuilt engine, is a rare opportunity for anyone who appreciates vintage motorcycles.