The way to preserve a building in architectural purity for 150 years is to spare it from "improvements" by making sure nobody wants to spend any money on it. So it was lucky, in a sense, that the London Town Public House in Edgewater, Maryland, became the Anne Arundel County alms house in 1828 and served in that capacity until 1965, when presumably there were too few poor to keep it occupied.

It stands today as a pristine example of a colonial structure of the 1740s, when it was built as an inn and tavern for travelers between Williamsburg and Philadelphia who stopped there for the ferry across the South River. The brick, the exterior doors and much of the glass are original.

There's no record of London Town's founding, or of its early days, but it was a thriving settlement in 1683 when it was designated a port of entry, primarily in tobacco trade, and it flourished for almost a century when it lost out as a tobacco inspection port to towns farther south, nearer the plantations.

The house and eight acres of grounds were designated a national historic landmark in 1970, and since then the Anne Arundel County Recreation and Parks Department and a citizens group called the London Town Assembly have been furnishing the building, restoring the gardens and a 1720 log tobacco barn donated by the A.B. Abell Co. of Baltimore. The assembly sponsors research into colonial life and holds workshops and special days re-creating colonial lifestyles.

This weekend, London Town is holding Market Days, with costumed docents guiding tours, craft demonstrations, plus food as served at an 18th-century fair, produced in part in the center's old crops garden.

The other gardens include sections of hollies, native azaleas, camellias and vibernums, a rhododendron slope, cherries and a wildflower section. Plants and herbs, including many now-rare descendants of 18th century varieties, are sold in the greenhouse.

Prices of the food served this weekend will differ from 1746, when prices for provender were set by the circuit court. The rates at the inn in 1746: A Quart of Rum 0.4.0 A Quart of Rum made into Flip with Brown Sugar 0.4.6 with double refined sugar 0.5.0 Cyder, Quince Drink of Perry pr Quart 0.0.6 A Nights Lodging in a Bed 0.0.6 A Hot Meal of Victuals 0.1.3 A Cold Meal of Ditto 0.0.9 Hay, Corn Tops for a Horse pr Night 0.0.6

The prices probably are pounds, shillings and pence. But inns as often as not took barter goods instead of cash. As a yardstick, an inn in Delaware at that time bartered a "bod of butter" (about 1 1/2 pounds) for a quart of rum.

Innkeepers at the Publik House, such as Mehitabel Holland and David Mackelfresh and Hester Groce, did more than feed and lodge travelers. Their establishments were the hub of town activity and they served as postmasters, market managers for itinerant craftspeople such as cordwainers and candledippers, bailiffs (since inns often doubled as courthouses) and newspaper mongers. Interns sponsored by the London Town Assembly are researching county records to document all the roles.