On even a cursory inspection the Forum is seen to lack unity in the details of its plan and in its architecture; the fact soon becomes apparent that it reached its final form only as the result of a long period of development. It will be worth while briefly to trace this development, and to note at least the more important changes which followed one another in the course of the centuries. In the earliest times the Forum was merely an open square bounded by four streets. [Illustration: Fig. 13.--North end of the Forum, with the Temple of Jupiter, restored.] The proof that this was the original form is in part based upon the orientation of the temple of Apollo. The sides of this temple have the same direction as the north and south streets in the northern part of the city, and must have been laid out parallel with a street that once ran between it and the Forum. The temple is, therefore, older than the colonnade of the Forum, which shows a marked deviation from the line of its axis; the divergence, as may be seen on our plan, was in part concealed by making a difference in the thickness of the pillars between the court of the temple and the Forum. It is obvious that the colonnade on the west side takes the place of an older street; the south side was probably defined by the prolongation of Abbondanza Street toward the southwest. Near the southeast corner an inscription was found: _V[ibius] Popidius Ep[idii] f[ilius] q[uaestor] porticus faciendas coeravit_, 'Vibius Popidius, the son of Epidius, when quaestor caused this colonnade to be erected.' No clew to the date is given, but it must have been before the coming of the Roman colony, for after that time there was no office of quaestor in Pompeii. It must also have been before the Social War; in those years of tumult an extensive colonnade would not have been built, and when the national spirit was so vehemently asserting itself, we should expect to find inscriptions upon public works in the Oscan language, certainly not in Latin. But the use of Latin may very well date from the latter part of the period of alliance with Rome; we may then with much probability assign the inscription to the second half of the second century B.C. Remains of the colonnade of Popidius are still to be seen on the south side, and on the adjoining part of the east side, extending just across Abbondanza Street; traces of it are found also on the west side, where it was afterward replaced by a new structure. On the east side north of Abbondanza Street no traces remain; the appearance of this part of the Forum was entirely changed when the four buildings (K, L, M, N) with their porticos were erected, but we can hardly doubt that the original colonnade extended here also. Our illustration (Fig. 14) shows the arrangement of the Doric columns in the lower story; of the Ionic columns above only scanty fragments have been recovered. The appearance of the whole may be suggested by our restoration (Fig. 13).