I think this would be the 'Front Quadrangle'

From the College website -
"Merton College, the first fully self-governing College in the University, was founded in 1264 by Walter de Merton, sometime Chancellor of England and later Bishop of Rochester. Mob Quadrangle, the oldest quadrangle in the University, was built in three phases: the Treasury c.1288-91, the north and east ranges and the Sacristy c.1304-11, and the Library on the south and west sides 1373-8. Mob Library is the oldest continuously functioning library for university academics and students in the world. The Gatehouse dates from the early fifteenth century, when Henry V granted a royal 'license to crenellate', which allowed for the construction of the battlement tower above the present-day lodge."