Despite being built with "leftovers," the 126-year-old Assembly Hall is an impressive, though often overlooked, structure on Temple Square.

Constructed mostly with cast-off stone from the building of the Salt Lake Temple of The Church of Jesus Christ of Latter-day Saints, the Assembly Hall was officially dedicated in 1882.

Although the Assembly Hall's granite rock came from the same quarry in Little Cottonwood Canyon as the granite for the Salt Lake Temple, its stones were not cut as precisely as those for the temple. Hence, the Assembly Hall has a rougher and darker texture with greater spacing between blocks.

The Assembly Hall, built by pioneers beginning in 1877, is described by the church's Web site as "a charming Gothic-style building with lovely stained-glass windows." It can seat 1,200 people, and has a main floor and balcony. That compares to 4,000 people in the Tabernacle and 21,000 in the Conference Center.

Often overshadowed by the larger Tabernacle or the modern Conference Center, the Assembly Hall has a fascinating history — though it isn't widely known.

It was built to provide a more efficient structure that could be heated in the winter, according to the Mormon Historical Sites Registry and the church's Ensign magazine. President Brigham Young announced plans to build the Assembly Hall at a priesthood meeting in the Salt Lake Stake on Aug. 11, 1877 — just 18 days before he died.

Initially, the building was mostly for meetings of the Salt Lake Stake. The spacious interior of the Tabernacle defied heating technology of the day. The Assembly Hall was smaller and boasted a steam heating system, piped under alternate benches throughout and with a dozen radiators against the interior walls.

The hall also was superbly lighted in its early days, with 24 gas lamps and a gigantic chandelier with 12 gas jets.

So, if Sunday was a cold winter day, meetings would often be held in the comfort of the Assembly Hall, instead of the cold Tabernacle, according to an 1882 report in the Deseret News.

It is likely this practice lasted through much of the rest of the 19th century. Fewer members likely attended meetings on cold winter days, and so the smaller Assembly Hall was probably adequate in size.

Led by Henry Grow, construction on the Assembly Hall lasted about three years. Church members in the Salt Lake area were encouraged to donate at least one day's labor toward its construction.

The "Bowery," a series of poles and braces supporting tree branches to block the summer sun, was the first structure to occupy the southwest corner of Temple Square, where the Assembly Hall is today.

The adobe "Old Tabernacle" was located there from 1852 to 1877; it seated 2,500. The Salt Lake Tabernacle opened in 1875.