The basic idea had been around since the time of King Solomon or before, but it was not until 1975 that Bertram Miller decided the ancient tradition of building a wall around a Jewish city could be revived in northwest Baltimore.

The wall Miller envisioned, however, would bear little resemblance to its biblical predecessors. It would be a wall without bricks, a wall without mortar or cement, a largely invisible wall that would keep no one out and yet, on the Sabbath, keep the Orthodox Jewish community in.

Now on the verge of completion, Miller's wall seems to a casual eye to be little more than a 14-mile-long, jury-rigged concoction of highway fences, telephone wires and clothesline, threading its way around and above the streets where as many as 75,000 Jews live.

But to the practiced eye of an Orthodox rabbi, this melange of materials has been fitted in a precise configuration that conforms almost completely to the ancient strictures set down by Solomon when he founded the institution of the wall, known in Hebrew as "eruv."

Meeting the complex Talmudic requirements governing the institution of "eruv," however, proved to be almost easy, compared with the complex and worrisome business of dealing with such secular concepts as rights of-way, air rights and insurance.

"You can appreciate the difficulties of going to an insurance agent and saying, "I want to insure an imaginary wall against the hazards of liability," the 33-year-old Miller explained recently in deadpan tones. "For a long while we were unable to get anywhere."

Still, Miller and some 20 other "eruv" supporters felt they had to preserve, for when the wall was completed, Orthodox Jews in the enclosed areas of northwest Balitmore and nearby Balitmore County would be able to perform small tasks out-of-doors on the Sabbath without violating religious law.

"The laws of carrying were given to Moses by God, and expanded on by Somonon," Miller explained. In Exodus 16:29 it says, '. . . Let no man go out of this place on the seventh day.' And in Jeremiah 17:21 it says, "Thus says the Lord: Take heed for the sake of your lives and do not bear a burden on the sabbath day or bring it in by the gates of Jerusalem. And do not carry a burden out of your house on the sabbath day or do any work . . .'

The 'place' refers to the actual place where a man is. If you're living in a place like a walled city, you can carry within the gates of the city," he explained.

The idea of constructing an "eruv" came to Miller after he read of a similar, successful effort by a group of Orthodox Jews on Staten Island; other small "eruvs" already existed in such locations as Queens, N.Y., Toronto and Miami.

In Silver Spring a few years ago a group of young, devout Orthodox Jews worked with two rabbis to put together a 12-mile-long "wall" around the White Oak and Kemp Mill area, using utility poles, telephone lines and fences along the Beltway, Georgia Avenue, New Hampshire Avenue and Randolph Road.

"Earilier there was a small 'eruv' around the White Oak Apartments," explained Orthodox rabbi Gedaliah Anemer of Silver Spring's Young Israel congregation. "Now they're a part of this."

"A very natural question to ask was, 'Why not here in Baltimore?'" said Miller, who teaches math at Woodlawn High School in the Balitmore suburbs. "But the way our society is organized a group of laymen just can't go out and undertake something of this magnitude."

The Orthodox rabbis first approached by Miller and some 20 friends, however, were skeptical. "They were afraid that construction of an "eruv" would lead to various types of backsliding . . . that some less committed persons would desecrate the Sabbath, for example playing tennis within the "eruv" boundaries."

To alleviate these fears and to show the extent of his support, Miller persuaded a rabbi to commission a survey of 600 Orthodox families in the affected area. Of the 300 questionnaires returned, Miller said, 96 percent favored an "eruv."

The rabbis agreed to go ahead, and Miller and his friends went to work.

"We took a survey. We essentially formed a survey committee . . . We knew essentially the area we wanted to enclose. We went out with the objective of enclosing the greatest area with the least amount of work," Miller said.

To start with, that meant finding existing structures that would be used as part of the "uruv." The utility wires lining six miles or more of the route were just such a structure; so were the fences lining the two major highways that formed partial boundaries of the enclosed area: the Jones Falls Expressway and the Baltimore Beltway.

Their job was also made a little easier by some of the biblical definitions of an "eruv," specifically those that permit doorways within a wall, even if there are more doorways than wall.

"Your conception of a wall and my conception of a wall are pretty much the same," Miller explained. "A wall is a wall. But a wall can have doorways. It doesn't lose its significance as a wall if it has doorways . . . . One type of 'eruv' is to build a stone wall around your city. But it is very different in the 20th century in an American city . . .

"However, a series of telephone poles and wires, modified slightly, can give you a series of door outlines -- we call this 'tzuras hapesach' -- and if you meet the strict requirements, you can carry within the wall formed by those doorways."

But, while they set out to meet the requirements of the Talmud, Miller and his friends found out along the way that they would have to meet the requirements of the Maryland Baltimore Gas & Electric Co. if they wanted to use highway fences or utility wires as part of their wall.

"We had some obstacles to overcome -- chiefly whether what they wanted to do would meet our legal requirements," explained Harry Pistel, the district engineer for the Baltimore office of the State Highway Administration. "If they attached anything to our fences, we had to make sure it wasn't hazardous."

Then, he added, the fence [along the beltway] doesn't go across some existing roads and in one place it isn't there. They used existing utility poles there, I think. They had to put wires on some of the poles to meet religious requirements," Pistel said.

"It wasn't adequate for us just to say, 'Oh, well, you've got a beltway fence.' We actually sent people into the bushes to make sure that the beltway fence was there," Miller said. "And that it was complete and continuous and also that there had been no erosion underneath that would render it invalid as an "eruv."

"So we sent PhD biologists and some teachers and lawyers and physicians and economists and chemists and accountants out into the woods with various types of clippers and sticks and so on . . . . These roads were built 20 years ago and there's never been any cutting back of the bush . . . . It was like blazing a trail through the Amazon. But this was done."

"In the areas where the fence did not come close enough to the ground to meet our strict definition, we received permission to make repairs, free of charge to the state," Miller added.

The definitions governing the institution of "eruv," Miller said, form a full tractate in the many-volumed Talmud. "A wall," Miller said, "must be at least 10 handsbreadths -- 40 inches -- above the ground. You can't have a wall starting two feet off the ground because you can get under it and it's not a wall anymore.

"In regard to the door outlines, our strict definition is that the wire, the horizontal -- the English word is lintel -- must run directly overtop of the two verticles -- essentially the two doorposts. Here you're talking about distances less than one-eighth of an inch. Part of our work is using standards to determine the precise alignment of the verticals in regard to the horizontal.

When BG&E's wires did not conform to the laws, the "eruv" backers strung their own plastic rope high above the streets, using BG&E's poles.

"I had a difficult time with this business at first," said BG&E engineer Albert Donnelly, assigned by the utility to work with Miller. "I'm a Methodist and I couldn't understand it.

"Also, we wanted to make sure it was safe, that none of our men would get hurt working near their lines . . . . When I got that cleared up I got the approval of management.

"My guess is they are using about six miles of our poles -- that's about 250 poles." About 10 percent of the length of the poles, he said, had been strung with the plastic rope of the "eruv" supporters, since the utility wires were hung in the wrong configuration.

G. H. Chabot, a senior engineer for the Chessie system, was, like Donnellly, somewhat taken aback when Miller approached him and asked for permission to string plastic rope 25 feet above the right-of-way of the Western Maryland Railway.

Chabot passed the work along to utilities engineer S. W. Sargent, who made up a standard agreement form with "Eruv of Baltimore Inc." -- a firm that Miller heads -- for the standard price: $50 for the agreement, and $45 a year for the lease of the Chessie's air rights.

"We do this with utilities all the time, but this was one of a kind," Sargent said.

That was the way insurance agent Donald Hannahs looked at it when one of Miller's coworkers, Stanley Lustman, approached him and asked for liability insurance for the "eruv," which the state highway adminsitration was requesting.

"I know the Old Testament," said Hannahs, a fundamentalist Christian, "so I knew what he was talking about. But none of my companies would take it. Most underwriters say, 'What's your experience with this?' And there isn't any. Then I found an underwriter who had studied the Old Testament, and he said, 'I'll find something.'

Eventually, Nationwide wrote out a $1 million liability policy for Miller and his "eruv."

There were many other details -- arranging for the use of city light poles where BG&E had no poles; buying poles where no otheres of any kind existed, and, as word got around, persuading people that their "wall" would get in no one's way.

Then there was the question of finding a rabbi to inspect the wall each Friday before the Sabbath begins at sunset to make sure it is intact, and setting up a telephone recording that would give Orthodox Jews the results of this weekly survey.

This month, Miller hopes, the last piece of rope will be hung and the "eruv" will be complete several thousand dollars and five years' worth of weekends since the time it was begun, and 25 centuries since Jeremiah reiterated Solomon's laws.

"But if you listen to me, says the Lord, and bring in no burden by the gates of the city on the sabbath day, but keep the sabbath day holy and do no work on it, then there shall enter by the gates of this city kings who sit on the throne of David riding in chariots and on horses . . . and this city shall be inhabited forever" -- jeremiah, 17:24-25.