SAN ANTONIO — Alamo officials have discovered a clue to the building's mysterious past, right over the doorway some 3 million visitors pass through each year.

Experts believe "1802" might have been scratched into the wall when the Alamo was a mission under Spanish rule, or perhaps decades later, after the U.S. Army added a second floor and roof in the mid-1800s.

Or, as Alamo historian and curator Bruce Winders suggests, it could have been left by an Alamo defender who kept watch from a ledge by a window during the 1836 siege and decided to mark the year of his birth.

More than likely, it's evidence of a little-known period between 1793, when Mission San Antonio de Valero was secularized, and 1803, when Spanish troops began to occupy the former mission that later would be known as the Alamo, Winders said.

"If you look at historic graffiti at face value, people usually put the date when they did it," he said. "Americans at that time were kind of notorious for leaving behind something that says, 'I was here.' "

Intriguing finds

The Alamo's on-site conservator, Pam Jary Rosser, made the discovery last week while removing dust and mold from a wall with a sponge and distilled water.

She spotted the date, the earliest ever found in the building, etched in numbers nearly an inch high into the mission-era plaster and limestone wall.

Also by the window above the Alamo's main doorway were etchings of "WVA," and what appears to be "54" or "SA," and "TEX." Since "W" rarely is used in Spanish, and West Virginia didn't become a state until 1863, Winders could not explain the markings.

The find was the latest of several intriguing discoveries Rosser has made while working as the Alamo's on-site conservator for more than a year.

Using ultraviolet light

As a contractor in 2009, she uncovered an arched doorway leading to one of the side rooms of the Alamo that dates to the 1700s. She and her mother, Cisi Jary, also discovered remnants of mission-era frescoes about a decade ago.

Rosser said it's exhilarating to find clues to the past at the Alamo, which is filled with markings and etchings, including many that can be seen only with ultraviolet lamps.

Some historic graffiti she's uncovered might date to the Civil War era. Alamo officials believe markings in ink or paint might have been left by the Knights of the Golden Circle, a secretive organization in the South that had a chapter in San Antonio.

Thursday's announcement of the discovery came less than a week after Gov. Rick Perry signed a bill giving the state oversight of the Alamo for the first time in 106 years.

Though some members of the Daughters of the Republic of Texas opposed the change, the organization has officially embraced the new law and appointed a transition team to forge an agreement with the General Land Office to remain as Alamo custodians.

Millions needed

The organization recently adopted a master plan for the state-owned Alamo complex that identified a need for $19.8 million in restoration and maintenance work, including $11.2 million for the Alamo church.

DRT President General Karen Thompson said the organization hopes to work with the land office to keep doing preservation work "that is adding to what's in our history books."

The Daughters are refurbishing the shrine, adding a gray sealant to its ceiling for appearance and to keep out rainwater.

In response to concerns about structural stability, the DRT hired a contractor to investigate the flat roof on the building's north side, to see if it needs more steel reinforcing.

Crews are soon expected to begin applying an acrylic waterproofing product called Hydro-Stop to the vaulted portion of the roof's exterior to control leaks.

An engineer's report has called water intrusion the "single largest threat to the continued viability of the Alamo structure."