SAN FRANCISCO (Tribune News Service) — Westerners brought many things when they came to the Bay Area. Among these was paranoia — a fear of others slipping in and disrupting the nice life they were making.

The focus of this paranoia was a mile-wide strip of water below what’s now the Golden Gate Bridge. If you look at a map of the San Francisco Bay, it’s like a vast front door left open to anybody who wants to cruise in and poke around. Early on, the concern was a British invasion. Then it was the Confederate States Navy — it existed and not just in the South — and then Japanese and German forces during World War II.

Several measures were proposed to guard this entrance. A never-realized idea from the 1860s was to string a cable all the way across the water to clothesline ships, professional-wrestler style. There actually was a physical barrier during the 1940s — a retractable metal-mesh net — to snag intruding U-boats. None was ever found in the Bay, so supposedly it worked, no doubt to the annoyance of larger marine mammals.

The most practical solution was a fort. The Spanish, realizing the narrows were key to controlling the region, built one called Castillo de San Joaquin in 1794. It was a funny-shaped adobe structure that could rain down fire from a perch roughly 100 feet above the water. When the Americans captured California in the mid-1800s, they wanted a fort closer to water level to bounce cannonballs over the waves like deadly skipping stones. Hundreds of workers — many of them miners who got skunked in the Gold Rush — physically lowered the ground, excavating the building site to just above Bay level.

Thus was born Fort Point, now a U.S. National Historic Site, an enormous expanse that invites exploration outdoors — on the grounds, atop the rooftop where cannons were once mounted and in the open air parade grounds at the fort’s center — as well as inside.

The four-story building, despite being made from millions of bricks, looks rather humble in the bridge’s massive shadow. But in its time, it was a mighty presence, one that might make a Confederate soldier wet his trousers.

“This was the only fort of its kind built west of the Mississippi,” said John Martini, a retired National Park Service ranger. “There were about 40 forts built with this general design scheme, but they were along the Atlantic and Gulf coasts. That the government spent money to build a cutting-edge coastal fort way out here in the wilds shows the importance of California during the Gold Rush.”

Martini knows the fort well, having worked there in the 1970s and written two historical books about it. “The idea was to build multiple-story forts, so that cannons could be stacked one upon the other to maximize firepower,” he said.

The fort employed four types of uniquely devastating cannonballs. The first was a plain old hunk of iron that flew at a thousand feet per second to smash through the oak walls of warships. Another was a metal eggshell filled with powder that could explode into shrapnel, and a third was a sack of grapeshot that tore up rigging like a giant shotgun blast. The last was also solid iron, but heated until red-hot in a furnace so it would light ships on fire.

Cannonballs from enemies would simply ricochet off the fort’s 5-foot-thick carapace. It was both a formidable defense and, to this day, an enduring example of the mason’s art.

“They didn’t have diesel-powered machinery swinging around the blocks of granite. It was all done with portable cranes and either strong backs or wheel power. The fact they were able to build the thing as fast as they did — they started in 1853, and it was almost finished in 1861, when the Civil War began — is remarkable,” Martini said.

“I’m such a nerd,” he added, “that I walk around looking at the arched ceilings and notice how the bricks were hand-cut at very specific angles to form intricate arches. It was done without electrical or hydraulic machinery and was just laborious. I don’t think it’s a craftsmanship we see much of nowadays.”

During the Civil War, the fort was occupied by dozens of soldiers, cooks, surgeons, laundresses and prisoners with 12-pound balls attached to their legs. By most accounts, it was not a nice place to stay. A contemporary sanitary inspector wrote:

“This Fort, as is well known, consists of a mass of granite and brick, situated at the entrance of the Golden Gate, presenting a bold front to the Ocean. And while its massive walls afford safe protection to its big guns, its interior arrangements offer but a cold and cheerless habitation to the soldier.”

Dense fog enveloped the grounds for 260-plus days a year. It kept the walls damp and the floors puddled with water. Soldiers tried to stay warm by burning fires with wood carried in from the Presidio. Nevertheless, the persistent clamminess — not helped by straw-filled beds and blanket rationing (one on your first year of enlistment, a second in your third year) — led to bronchitis, rheumatism, diarrhea and catarrh, aka an excess of mucus.

“They would’ve worn a wool cape and sometimes, they’d have whale skins to wear or the Civil War kepi (hat) with a rainproof cover,” Martini said. “But even when it’s rainy, you have to keep walking, just keep slogging.”

What was the result of their vigilance? Well, Fort Point and other batteries on the hills and atop Alcatraz Island famously never fired a shot in anger. Its mere presence, however, was seen by military officials as a deterrent to incursions. While paranoia was high when it was manned periodically from the Civil War through World War II, those fears were not unfounded.

In 1863, the United States captured a Confederate privateer prowling the area, presumably to steal gold shipments. And there were definitely Japanese submarines off the coast. “There was one somewhere between the Cliff House and the Farallons,” Martini said. “It had orders on Christmas Eve of 1941 to surface and, using its deck guns, just randomly shell San Francisco as a terror move. It never did — it got a recall order many hours before the shelling began, so they just returned to Japan.”

The threat level around then was so great, it might have affected the whale population. “The Navy used to run blimps, loaded with depth charges, patrolling off the coast looking for submarines. Based on a few reports, some whales might have met their end that way. When you consider everybody’s war jitteriness, and you consider a big, gray object just off the coast, it’s possible.”

The fort’s purpose as a functional defender of the Bay was short-lived. Around the beginning of the Civil War, cannonballs became obsolete, replaced by pointed artillery that was extremely accurate and could drill through masonry walls. After its service in WWII, the fort became a military warehouse and then in 1970, a designated historic site, with subsequent appearances in films, including 1985’s James Bond flick “A View To a Kill” and 2014’s “Dawn of the Planet of the Apes.”

“I always asked people when they’re there, especially when it’s a gnarly weather day, to think about what it’d be like to stand patrol on the top tier,” Martini said, “walking post for four hours at a stretch, waiting for an enemy that never came.”

Admission is free at Fort Point, which is open from 10 a.m. to 5 p.m. Friday-Sunday (roof access closes at 4:30 p.m.), with ranger talks offered at 11:30 a.m. and 1:30 p.m. The fort exterior can be accessed seven days a week. Find the fort at Long Avenue and Marine Drive in San Francisco; www.nps.gov/fopo/.

©2023 MediaNews Group, Inc.

Visit at mercurynews.com.

Distributed by Tribune Content Agency, LLC.