[3] Calvi designed a wall that ran west–east in a straight line from the coast for about 280 metres (920 ft) until it reached a precipice.

[4] Philip II of Spain succeeded Charles V in 1558, and commissioned the Genoese engineer Giovan Giacomo Paleari Fratino to continue the improvements to Gibraltar's fortifications.

El Fratino decided that the traverse should be abandoned, and that the work already completed on Calvi's zigzag wall should be demolished.

[5][6] A 1786 book described the defenses as follows: Above the precipice, an old Moorish wall is continued to the ridge of The Rock; in front of which a curtain with loop-holes and redans (built in the reign of the Emperor Charles V, and called after his name) extends to the top, effectually cutting off all communication in that quarter.

Between the Moorish and Charles the Vth's walls, is the signal-house; whence the guard, on a serene and clear day, have almost an unbounded view of the Mediterranean...[7]Notes Citations Sources