  Using the combined capabilities of the large near-infrared Palomar/DEEP-2
survey, and the superb resolution of the ACS HST camera, we explore the size
evolution of 831 very massive galaxies (M*>10^{11}h_{70}^{-2}M_sun) since z~2.
We split our sample according to their light concentration using the Sersic
index n. At a given stellar mass, both low (n<2.5) and high (n>2.5)
concentrated objects were much smaller in the past than their local massive
counterparts. This evolution is particularly strong for the highly concentrated
(spheroid-like) objects. At z~1.5, massive spheroid-like objects were a factor
of 4(+-0.4) smaller (i.e. almost two orders of magnitudes denser) than those we
see today. These small sized, high mass galaxies do not exist in the nearby
Universe, suggesting that this population merged with other galaxies over
several billion years to form the largest galaxies we see today.
