The Towne mansion stood on Nob Hill, part of the cluster of railroad-baron estates that defined the hilltop before the earthquake. When the 1906 fire swept through, the mansion was destroyed along with nearly everything else on Nob Hill. The marble entry portal survived because stone does not burn. It was photographed amid the ruins, framing a view of the devastated city beyond, an image that became one of the iconic photographs of the earthquake's aftermath. The portal was later moved to Golden Gate Park and installed at the edge of Lloyd Lake, where its classical proportions and the accident of its survival transformed it from rubble into art.

The portal's placement at the lakeshore was no accident. Positioned so that visitors approach it from the park's paths, it creates the illusion of a doorway opening onto the water. The effect is startling: a formal architectural element, designed to welcome guests into a mansion, now welcomes them into nothing, or into everything. The absence behind the portal is the point. The mansion it belonged to is gone. The neighborhood it stood in was rebuilt. The people who walked through it are dead. What remains is the gesture of entrance, preserved in marble, a permanent threshold leading to the past.

Portals of the Past has become one of Golden Gate Park's most recognized landmarks, though many visitors pass it without knowing its story. It is listed as a San Francisco Designated Landmark. The columns are weathered now, their marble softened by more than a century of fog and rain. Lloyd Lake reflects them in the early morning, doubling the image. Photographers come for the light. Joggers pass without pausing. The portal asks nothing of anyone. It simply stands, as it has stood since a fire burned away everything around it except the part designed to be walked through.