Many public buildings in the United States have cornerstones featuring the date as well as an "AL" followed by a number. The AL is the abbreviation of the Latin words anno Lucis, meaning "in the year of light." It is similar to the AD, which means anno Domini or "in the year of the Lord."

Free and Accepted Masons, who conduct the cornerstone ceremonies, put the AL on the stone as their means of marking the passage of years. The date refers to the moment described in Genesis when God created light. In 1650, Archbishop Ussher of Northern Ireland used genealogies and other evidence in the Old Testament to determine that God created the universe in 4004 BC. A later scholar, Dr. Lightfoot of Oxford, refined that calculation, concluding light dawned in the universe at 9:00 a.m., on October 23, 4004 BC.

Some older cornerstones use the 4004 date as the benchmark, adding that number to the current year, AD. Most modern cornerstones cast aside the precision and round it off to 4,000 years, so a cornerstone set in AD 1999 also has the date AL 5999.