Ah, the good old days before doorbells. A time when announcing your arrival at someone's home required more than an impotent little chime. Back in the medieval days, it took an ample amount of engineering, construction and, of course, a high-speed boulder aimed at your host's castle wall. Borrowing a working reproduction of a trebuchet catapult from the Virginia Military Institute, the Science Museum of Virginia invites guests to bring any items between 10 and 20 pounds to launch in some unspecified direction over the city. Bring crappy gifts so there's plenty of ammunition for an improvisational siege of Richmond. The assault starts Saturday, Jan. 3, at noon and continues through 4 p.m. Tickets are $9-$10. Call 864-1400 or visit www.smv.org.