SAN YGNACIO, Texas (AP) — Legends differ on the origins of the sundial over the arched gateway of the 1830s Trevino Fort, a cluster of timeworn buildings on the banks of the Rio Grande.

One says it was installed as a tribute to cosmology. A 10-year-old boy made his way back from a kidnapping by American Indian tribes, guided by the patterns of the stars.

The atypical flourish is just one curiosity in what historians call the most significant, and amazingly intact, piece of Texas-Mexico border history still standing.

The building style is Spanish, its simplicity a testament to the hardships of what became the northern Mexico, then southern Texas, frontier. Its walls predate the U.S.-Mexico border to a time when Spanish land grants straddled the Rio Grande and settlers did business in cities such as Guerrero and Camargo. Its existence points to the deadly tensions between European settlers and native tribes, particularly concerning the waters of the Rio Grande.

"It really embodies in one place, in one structure, the history of the border," said Mario Sanchez, an architect who edited the book "A Shared Experience" in 1994 as part of a project commemorating the binational history of the Rio Grande.

"Let's face it, it was built by people across the river to tend to their lands on the north banks," he said. "It's there in wood and stone. Architecturally, historically and culturally, it is extremely significant. ... It is a step back in time."

San Ygnacio was established by Don Jesus Trevino, a land claim purchaser who settled in Guerrero, Mexico, and wanted a fortified dwelling for ranch hands north of the river.

His son-in-law, Blas Maria Uribe, set up housekeeping. Other settlers took refuge and manned the troneras, or gun portholes, during attacks by indigenous tribes.

Descendants of the Trevinos and Uribes, as well as families with the names Benavides, Martinez and Gutierrez, remained for generations. Some still occupy homes there.

Unlike nearby towns Zapata and Guerrero Viejo across the river, the fort was spared the flooding that came with the new Falcon Dam. It also withstood 1967's Hurricane Beulah.

But if it weren't for artist Michael Tracy, who took up residence near the fort, the deteriorating structure might not have survived the past decade.

Tracy and colleague Christopher Rincon established the River Pierce Foundation to raise funds to purchase the structure, with the motto of "crossing borders of awareness by bringing awareness to the border."

"We bought half of the fort in 1998 and took 10 years to get the other half," Tracy said.

Over the years, their efforts earned grants from the National Trust for Historic Preservation's Fondren Fund and donations of money and expertise from the Brown Foundation Inc. of Houston, the Texas Historical Commission and the local Guadalupe and Lilia Martinez Foundation. The Center for Heritage Conservation at Texas A&M; has helped with a master plan for what may be several phases of restoration.

A key victory came in 1998, when the fort was designated a National Historic Landmark. Last year, enough money had been raised under the Historical Commission grant to begin emergency stabilization.

Architectural historian Terri Myers said San Ygnacio is the largest, and most intact, collection of Spanish descendant architecture in the U.S.

"Michael Tracy and Chris practically spent their life trying to acquire the fort. It's kind of remarkable," she said. "I don't think they get a lot of support. Sometimes it seems people far away recognize the value of the place more than people here. They may see it is as just a dusty little town with flat-roof houses. What they don't realize is that, hey, it doesn't exist anywhere else."

Texas A&M; archaeologist Alston Thoms said the settlement offered clues not just about the border's Spanish heritage but about the Rio Grande "life way," which he thinks retains evidence of human habitation dating back 15,000 years.

Recently, as Rincon showed visitors the barely decipherable etchings on the fort walls and a curious daisy-shaped sculpture, the stone font for holy water, Tracy stormed in, frustrated that a bank had turned down a donation request.

These are hard times to raise money for history's sake, he said, particularly with a remote and at first glance unassuming fort.

"This is humble, and humble is a hard sell," Tracy said.