Sekisho means check point in Japanese. Until the end of Edo period (1603-1868), Japan had been holding many regional powers and they are administered by Edo Bakufu, the central power located in Edo, today's Tokyo. Sekisho was a check point equipped on the border line between different regional powers.
Sekisho, needless to say, has no longer been used as check point since Meiji new government was established. During Edo period, about fifty official Sekishos had been existing while there had been so many minor or private ones. Fukushima Sekisho had been one of the four major sekishos.
The first ever sekisho system is confirmed on documentary materials published in A.D. 646 but the time that its existing is surely confirmed is some decades after that point. Then, in late medieval period, the system was abolished in the process of building centralized nation.
However, since Tokugawa Ieyasu has established Edo Bakufu and built more steady administration across Japan, the Sekisho system became necessary again for controlling the flow of people and various goods. Sekisho, therefore equipped again on strategically important points.
Sekisho was managed by lower class of samurai but traffic fare was charged impartially regardless of the status of passersby. Passage license was also required to them but entertainers were often permitted to pass sekisho by playing their performance instead of showing their passage license.
Edo Bakufu had been keeping their foundation of authority by having the local leaders come to Edo and having Bakufu's officials go to Local states (Han) for keeping their eyes on the activities of those states. Sekisho, therefore, had been playing an important role in their administration system.
The clip below is an example of the sekisho's composition (not Fukushima sekisho but Hakone sekisho). Sekisho was not just a gate but had some functional structures such as stall(stable), shooting barricade, and lookout tower.
Sensibly and interestingly, there were female officers to check women's belongings and bodies. Physical features of wanted men for crimes were noticed to every sekisho and violating its security check could become subject to execution.
In fact, 6 individuals were executed for sekisho breaking during Edo period. To prevent it, there were guard lodges on other trails and crapping traps were equipped in forests. In the late of Edo period, however, the business that assisted breaking sekisho emerged and the penalty for it was mitigated.