If anyone can shed light on the Lexington Town Tomb, I'd love to hear about it. Google turns up nada.
* Update. Several folks did more searching, and found explanations for general town tombs in New England. Here's what we know now.
" A town tomb was constructed in 1836 for the interment of the dead during winter months when burials were precluded by frozen ground. Three other similar tombs were later constructed for private burials. All four tombs were built into the earth, and because of this had access doors less than three feet high. Unfortunately, the tombs proved to be problematic for various reasons. The roofs leaked, the town tomb was too small to accommodate all of the bodies awaiting spring burial, and the small entry doors made movement of bodies in and out of the tomb difficult. Because of these problems, the Cemetery Commission requested the construction of a new tomb that would be entirely above ground and larger, a request that was carried out years later upon the grounds of Evergreen Cemetery. In subsequent years, all bodies were removed from the tombs and returned to the earth, so the tombs are empty today."