The checkpoints were controlling travel permits and were performing a strict control of guns, which were completely forbidden in Edo. Also, the domain lords families (wifes and daughters) were not allowed to exit Edo, were they were held by the Shogunate as hostages.
EXIF info:
Nikon D90
Lens: VR 18-55mm F/3.5-5.6G
Focal Length: 18mm
Aperture: F/5.6
Shutter Speed: 1/200s
ISO Sensitivity: ISO 200