Preheat oven to 450 degrees F. Trim the asparagus, arrange in rows of 6 spears, and poke two skewers perpendicularly through the rows. (The result will look like a raft.) Mix olive oil, garlic, and salt and pepper. Place asparagus on a broiler pan and drizzle with olive oil mixture. Roast, turning two or three times, until tender. Remove from heat. Wrap 4 spears in a slice of prosciutto and serve.