This summer thousands of tourists, residents and visitors will cross Eaglehawk Neck in southern Tasmania without much thought.

Key points: Savage dogs chained up in a line guarded against prisoners escaping from Port Arthur in the 1800s

Savage dogs chained up in a line guarded against prisoners escaping from Port Arthur in the 1800s It was felt the animals' hearing, sense of smell and vicious bite were more effective than sentries at detecting and deterring potential escapees

It was felt the animals' hearing, sense of smell and vicious bite were more effective than sentries at detecting and deterring potential escapees Known as the Dog Line, it was depicted in the fictional For the Term of His Natural Life

But, getting across the neck was not always so easy.

From the 1830s the remote Tasman Peninsula was under military rule, and home to a tough prison for Britain's most hardened criminals.

For a convict trying their luck to escape the Port Arthur Penal Colony, the only way out by land was through the narrow, sandy isthmus — or face treacherous seas rumoured to be shark-infested.

"The only part that was easy to escape from was across the neck," historical researcher Brian Rieusset said.

There had been escape attempts from the newly established prison, and Governor Arthur ordered sentries to be put in place to guard the neck.

A small military settlement was established at Eaglehawk Neck from 1831.

An art piece is the only reminder of the Dog Line. ( ABC Radio Hobart: Georgie Burgess )

Mr Rieusset said the sentries were not effective and their ears had to compete with the roar of the sea, so the officer in charge came up with a plan.

"Ensign Peyton Jones came up with the idea of putting dogs across the neck," he said.

"Dogs had good hearing and could detect anything."

The dogs were kept on chains and set up in a line across the neck with lights, known as the Dog Line.

Dogs were also put in place on elevated stages in the water, to detect convicts attempting to wade across.

"The dogs would hear anyone coming," he said.

Not only that, the dogs could smell the convicts — who were not known for their hygiene.

Peyton Jones also placed piles of shells across the neck which would crackle loudly if convicts walked across them.

Jones reported that during the 16 months he was there, "no man ever crossed the neck".

A sketch of the Dog Line. ( Supplied: Tasmanian Archives )

A line of 'savage dogs'

The Dog Line started off with nine dogs, but grew to 18.

They were a mixture of breeds, some reportedly bloodhounds.

"They got some pretty savage dogs," Mr Rieuesset said.

"They were tethered by chains so they could almost touch snouts and eat out of the same trough, but couldn't attack one another."

Mr Rieusset said a bold soldier attempted to pass through the dogs and suffered severe bites.

"No one could pass through without being bitten," he said.

"It was the perfect way to guard it."

A sketch of Eaglehawk Neck looking south showing the Dog Line. ( Supplied: Allport Library and Museum of Fine Arts )

In his research, Mr Rieusset found a description of the dogs by author Henry Melville from 1840 which said "every four-footed, black-fanged individual among them would have taken first prize in his own class for ugliness and ferocity at any show".

The dogs were well fed, and were handled by soldiers and trusted convicts who were trained to look after them.

"It was quite a status symbol to be a dog handler at Eaglehawk," he said.

Nowadays, the isthmus is the busy Arthur Highway, the gateway to the Peninsula's natural wonders and the acclaimed Port Arthur Historic Site.

Sir John and Lady Jane Franklin visit the Dog Line. ( Supplied: Tasmanian Archives )

Escape if you dare

Despite the Dog Line, there were still escapes from Port Arthur.

Most notably was infamous bushranger Martin Cash who managed to escape twice.

During his second and most successful escape he swan across Eaglehawk Neck, winning him respect from fellow inmates when he would inevitably return to prison.

"They used to tell a story that there were sharks," Mr Rieusset said.

On the set of 1927 film For the Term of His Natural Life, featuring the Dog Line. ( Supplied: Tasmanian Archives )

Another convict tried to escape by wearing a kangaroo skin and hopping across the beach.

Soldiers soon spotted the attempt and pointed their weapons at him.

"He gave himself up, he didn't want to be shot as a kangaroo," he said.

Mr Rieusset said other attempts involved convicts stealing the superintendent's boat at Port Arthur.

A more tragic story was a group of four who escaped Port Arthur and made it to Fortescue Bay and built a canoe.

The party almost made it to the Hippolyte Rocks, about eight kilometres out to sea from the bay.

"The boat sank, two of them managed to get back to shore, a third drowned somewhere out there and the fourth one who was a native of South Africa got almost back to shore but unfortunately drowned," Mr Rieusset said.

The escape scene from the film For the Term of His Natural Life. ( Supplied: Tasmanian Archives )

Dog Line movie fame

While little is written about the Dog Line, it featured in the 1927 silent film For the Term of His Natural Life.

The film was based on the book by Marcus Clarke, which tells the story of a convict escaping Port Arthur.

"Marcus Clarke did an amazing job to get people to appreciate the transportation system," Mr Rieusset said.

He said Clarke visited Tasmania and Port Arthur in the 1870s and was allowed access to convict records.

The records allowed him to accurately depict the life of a convict.

The Dog Line was included in the escape, with the protagonist sneaking through it.

"He gave Australia and the world an insight into what Port Arthur had been like," he said.