Some 1,500 years ago, the massive brick ramparts of Bamburgh Castle in Scotland girded against Viking hordes from across the North Sea.

Its military role long retired, the outpost recently was a stopover for media drives of the Bentley Mulsanne, an all-new sedan for the auto maker tasked with defending against another invader — the Rolls-Royce Ghost.

However, suggesting the $285,000 Mulsanne competes against the $245,000 Ghost draws nothing but grumbles from the folks at Crewe. After all, these British rivals have had pistols perpetually drawn since Volkswagen AG and BMW AG broke up their dysfunctional relationship more than a decade ago.

But bear this in mind: The Mulsanne plays atop Bentley's range, while the Ghost occupies the lowest rung at Rolls-Royce. Timing-to-market also roughly coincides, as do engine displacements and, as usual, the OEMs will fashion option packages for buyers' every desire.

So with its borders breached, Bentley brings the Mulsanne later this year to defend a cozy market segment the auto maker carved out for itself with the launch of the Continental range in 2003. The Mulsanne also effectively replaces the Arnage, which until now served as the auto maker's principle V-8-powered land yacht.

The Mulsanne, however, warrants little comparison with its predecessor. The two cars weigh the same, but the Mulsanne is faster and more fuel-efficient.

Initial driving impressions recall a fat uncle who always took up too much of the couch during the holidays. Creeping through the gates of Bamburgh Castle, — built to accommodate cavalry — takes assistance from public-relations staff.

Out on the maddeningly narrow rural roadways of the U.K, the Mulsanne's girth is no picnic for the uninitiated. With each passing lorry, the left front tire of the right-hand-drive Mulsanne goes “thumpety-thump-thump” along the shoulder.

But on wider roads, the Mulsanne starts working some old-school Bentley charm. Relax your shoulders into the buttery leather seat, ease into the throttle and watch the countryside blur past.

Calling the redesigned 6.75L pushrod V-8 responsive would be like calling the Mona Lisa pretty. With its 752 lb.-ft. (1,020 Nm) of torque available at just 1,750 rpm and twin turbochargers, the engine effortlessly propels the 5,700-lb. (2,585-kg) Mulsanne.

Variable-valve timing and an imperceptible cylinder-deactivation system improve efficiency.

An 8-speed ZF transmission shifts quickly and smoothly. Steering wheel-mounted paddle shifters, a first for Bentley, satisfy drivers wanting more interaction.

While this bruising sedan weighs more than a Chevy Tahoe fullsize SUV, the Mulsanne remains surprisingly nimble. A new chassis unique to the Mulsanne is lighter, stiffer and more technologically advanced than any previous Bentley.

Four specially tuned motoring modes are accessed via a dial near the gear selector to optimize suspension and steering.

Each mode works alongside the real-time air-assisted damping system, massive disc brakes with Bentley-branded calipers and 21-in., Z-rated tires that put a big confident patch of rubber on the roadway.

On a sprint through the Northumberland National Forest, where the roadway features tight switchbacks and sudden elevation changes, the Mulsanne handles admirably if not spectacularly, by bailing out drivers captivated by sprawling fields of Scottish heather.

Inside, the Mulsanne is quiet as a confessional. High winds off the sea prove no match for the air-tight cabin, and even the wiper blades glide softly across the windshield during a cloud burst.

Leather and wood dominate the interior, and Bentley's hand-crafted work is plainly evident. It's easy to imagine the employees at Crewe hand-stitching our tester's linen and redwood leather or running a plane across its Vavona wood trim.

The Mulsanne also embraces new technology. A handmade, leather-lined iPod drawer softly withdraws from the dash, unlocking a 14-speaker audio system of flawless sound quality.

Of particular note, the Mulsanne's redundant navigation screen inside the driver-information center easily ranks as the industry's most sophisticated.

Using a combination of arrows and voice commands, it's nearly impossible to take the wrong exit in a roundabout.

Old-world organ-stop pulls for opening and closing air vents serve as a pleasant contrast to such modern gadgets.

The exterior design is meant to recall the Bentley S-Type of the 1950s. It resembles a modern heavyweight boxer — a square jaw with broad, chiseled shoulders flowing to a taut mid-section. Its stance conveys the power of a haymaker and the quickness of a left jab.

Bentley executives expect the Mulsanne to account for 10% of annual sales, with 2010 deliveries tracking at 5,250 units.

While the Average Joe lost most of his retirement during the recession, the average Mulsanne buyer still sits on more than $25 million of disposable assets.

So as niche-ified as the Mulsanne might appear, it still provides a valuable lesson: Don't dally about when someone jumps into the ring.

Instead, deliver a knockout.