Susa. A Royal Road connected Susa with the more eastern capitals of Persepolis and Pasargadae in Persis (the Persian Empire had several "capitals"), and was the natural venue for Alexander's continued campaign. After the conquest of Susa, Alexander split the Macedonian army into two parts. Alexander's general, Parmenion, took one half along the Royal Road, and Alexander himself took the route towards Persis. Passing into Persis required traversing the Persian Gates, a narrow mountain pass that lent itself easily to ambush. Believing that, after his victory over the Uxians, he would not encounter any more enemy forces during his march, Alexander neglected to send scouts ahead of his vanguard, and thus walked into Ariobarzanes' ambush. Once the Macedonian army had advanced sufficiently into the narrow pass, the Persians rained down boulders on them from the northern slopes. From the southern slope, Persian archers and catapults launched their projectiles. Alexander's army initially suffered heavy casualties, losing entire platoons at a time. Ariobarzanes had hoped that defeating Alexander at the Persian Gates would allow the Persians more time to field another army, and possibly stop the Macedonian invasion altogether. Ariobarzanes held the pass for a month, but Alexander succeeded in encircling the Persian army and broke through the Persian defenses. The defeat of Ariobarzanes's forces at the Persian Gate removed the last military obstacle between Alexander and Persepolis. Upon his arrival at the city of Persepolis, Alexander appointed a general named Phrasaortes as successor of Ariobarzanes. Four months later, Alexander allowed the troops to loot Persepolis. A fire broke out and spread to the rest of the city. It is not clear if it had been a drunken accident, or a deliberate act of revenge for the burning of the Acropolis of Athens during the Second Greco-Persian War. Siege of the Sogdian Rock After Alexander defeated the last of the Achaemenid Empire's forces in 328 BC, he began a new campaign to Ariana in 327 BC. He wanted to conquer the entire known world, which in Alexander's day, ended on the eastern end of India. Greeks of Alexander's day knew nothing of China, or any other lands east of Bactria. The Siege of the Sogdian Rock, a fortress located north of Bactria in Sogdiana, occurred in 327 BC. Oxyartes of Bactria had sent his wife and daughters, one of whom was Roxana, to take refuge in the fortress, as it was thought