A.T. Robertson Commentary Matthew 27:66

"So they went, and made the sepulchre sure, sealing the stone, the guard being with them." — Matthew 27:66 (ASV)

Sealing the stone, the guard being with them (σφραγισαντης τον λιθον μετα της κουστωδιας). Probably by a cord stretched across the stone and sealed at each end as in Da 6:17. The sealing was done in the presence of the Roman guard who were left in charge to protect this stamp of Roman authority and power. They did their best to prevent theft and the resurrection (Bruce), but they overreached themselves and provided additional witness to the fact of the empty tomb and the resurrection of Jesus (Plummer).