Both Renault drivers taste Monaco wall
Rookie Nelson Piquet, who so far is off the pace in the Principality, was the first to lose control of the rear of his R28 during the second practice session of the day.
He half-spun and nudged into the turn one tire barrier with the rear of his car, but was able to nurse the ailing single seater back to the pits with a damaged rear wing.
Alonso, the former double world champion, did a similar thing at the same Saint Devote corner, but he missed the tire barrier with his left rear wheel and instead smacked the subsequent stretch of arm-co.
The Spaniard then briefly brought out the red flags when his damaged rear wing broke off as he was recovering to the pits.
Toyota's Jarno Trulli, after stopping in the morning following contact with the barrier, again lightly bumped into the wall in the final 90 minutes of Thursday practice as he exited the Swimming Pool.
Adrian Sutil also got into the wall at the beginning of La Rascasse, knocking off the front wing of his Force India.
One startled pitlane resident who was crossing the pitlane, meanwhile, was lucky to avoid being hit by the session's fastest man Lewis Hamilton, as the McLaren driver exited his pit garage.
Four tenths adrift, Williams' Nico Rosberg was a surprise second quickest, ahead of the two Ferraris and Hamilton's teammate Heikki Kovalainen.