Garrison for the Rammas Echor

[Gordis]

Walls were indeed efficient against raiders - but not against a huge advancing army. I understand why the Rammas had been built initially, but repairing and strengthening the wall in 3018-3019 was nothing but a waste of time and effort.

Also consider that if the Enemy hadn't destroyed the north-western part of Rammas Echor, but fortified and manned (orc-ed) it instead, the advance of the Rohirrim cavalry would have been stopped.

It looks like Rammas had been built after 2901

Gandalf passed now into the wide land beyond the Rammas Echor. So the men of Gondor called the out wall that they had built with great labour, after Ithilien fell under the shadow of their Enemy.LOTR, Minas Tirith

2901. Most of the remaining inhabitants of Ithilien desert it owing to the attacks of Uruks of Mordor. The secret refuge of Henneth Annûn is built- TY

Likely when Rammas had been completed, the Gondorians deemed it safe to rebuild the Bridge of Osgiliath (in ruins since 2475):

Yet we won [Osgiliath] back in the days of the youth of Denethor: not to dwell in, but to hold as an outpost, and to rebuild the bridge for the passage of our arms.- LOTR, Minas Tirith

Denethor was born in 2930. The bridge was likely built before 2951, the year when Sauron declared himself openly in Mordor, after that it would have been utter foolishness.

As it was, they now got the Bridge leading into the abandoned Ithilien (built a bridge for Sauron, so to say) and the Rammas that couldn't really guard Minas Tirith. Not too smart, precious...