The Meridian Fold is the largest of the Lost Blocks, encompassing approximately six square blocks in the heart of the Circuit District. It is named by Dr. Sato Mbeki-Larsen, whose Theory of Urban Cysts was inspired in part by the Fold's sheer scale — this is not a hidden courtyard or a sealed alley, this is a significant piece of urban territory that is visible from orbit and absent from the ground. The Fold contains an estimated 18 buildings, a network of streets, two plazas, and what satellite imagery suggests is a small market or commercial district. It is the most complex, the most populated, and the most active of all the Lost Blocks. It is also the one that is growing.

The Meridian Fold became inaccessible in 2207 — the earliest of the confirmed Lost Blocks. For nearly two decades, it has existed as a visible, thermally active, power-consuming ghost neighborhood in the center of the district. Thermal imaging shows approximately 120 heat signatures — the largest concentration of any Lost Block — engaged in daily patterns that suggest not just habitation but community. Signatures congregate in the plazas. Groups move together. There are patterns that look like social behavior, like commerce, like daily life conducted at a scale that implies organization.

But the Fold is growing. Dr. Anand-Petrov's decadal analysis shows approximately 7% expansion — the highest rate of any Lost Block. The growth follows the street grid, extending along existing axes. A building that was demonstrably outside the Fold in 2224 — a four-story commercial building at the corner of Meridian Avenue and Circuit Street, occupied by a data storage firm — is now inside it. The building's former occupants describe a sudden transition: they arrived at work on a Monday morning and the entrance was a wall. Their equipment, their files, their personal belongings — all inside, all visible on satellite, all unreachable. The insurance claim is still in litigation. The building is still inside the Fold, its windows visible from orbit, its doors accessible to no one.

Dr. Mbeki-Larsen's model predicts that the Meridian Fold is in an early acceleration phase. If the model is correct, the growth rate will increase before stabilizing at a boundary that the math defines but that no one wants to calculate. The Fold is the Lost Block that forces the question: what happens when the anomaly stops being something you can ignore? What happens when it swallows your office, your apartment, your street? What happens when it stops being a curiosity and starts being a crisis?