In what era did the hotel design of each room with a bathroom appear and become popular?

The hotel design of each guest room with a bathroom appeared and became popular in the early 20th century.

At the beginning of the 20th century, the world's largest hotel owner Ellsworth-Michel Every room in Statler's Statler Hotel had a bathroom and he established uniform standards to manage the hotels he opened everywhere.

In 841 BC, the first year of the First Emperor's reign of the Zhou Dynasty in China, the exchanges between the twelve feudal princes and scholar-bureaucrats became China's initial need for mobile accommodation.

From 400 BC to 200 AD, during the ancient Roman and Greek periods, in order to adapt to the increasing official and unofficial travel needs, the hotel industry began to differentiate into hotels that specifically served government postal services and government officials. There are two categories: "mail stations" and "inns" which mainly serve the general public.