because of the difficulties the construction of an underwater section would present, and the time it would require, it was planned in 1927 to link to line 10 an expansion of line 7 between "jussieu" and "porte de choisy" that was already underway. with this in mind, it was decided to create a connection with two platforms between the stations "maubert" of line 10 and "place monge" of the future line 7 such that line 10 borrowed this section of line 7 while the underwater tunnel that connected the northern and southern sections of the line was constructed.