But I saw nothing to cause a commotion among the watchers on the hillside. The siege towers and war machines were unengaged. No smoke rose from the city, and I saw no sign of fighting along the wall.

"There!" Antony pointed away from the city, toward the entrance to the harbor and beyond. A fleet of large ships was approaching from the open sea. Several had already reached the harbor entrance and appeared to be maneuvering to sail through in single file. I found this curious, as I had sailed in and out of Brundisium myself in the past, and knew that the harbor entrance was deep and wide enough for several ships to sail abreast, yet these were apparently endeavoring to enter one at a time, keeping as close to the center as possible.

As the first ship entered the straits, I saw the reason for such a course. The sight was so strange, I had trouble believing my eyes. At the narrowest part of the entrance to the harbor, great piers of some sort had been built out from both promontories, extending far into the water. This breakwater very nearly met in the middle, or so it appeared at a distance, almost closing off the entrance to the harbor. Short towers had been built at intervals along both arms of the structure, and these were equipped with catapults and ballistic machines.

"By my ancestor Hercules, what are we seeing?" muttered Antony, as puzzled by the sight as I was. He turned his head and scanned the other soldiers watching along the hillside. A bearded little fellow was standing atop a boulder nearby, viewing the scene intently with his arms crossed, mumbling to himself. Antony called out to him. "Engineer Vitruvius!"

The man blinked and looked in our direction.

"Engineer Vitruvius! Report!"

The man scrambled down from the rock and came running. He saluted Antony. "Tribune, you've rejoined us!"

"You state the obvious, Marcus Vitruvius. What's not so obvious is what we're witnessing down there. What in Hades is going on?"

"Ah!" Vitruvius looked toward the harbor, but was so short that the tops of some trees down the hillside blocked his view. "If we may retire to higher ground, Tribune…"

We followed him back to the boulder. He scrambled atop it, crossed his arms, and gazed down at the harbor. "Now, Tribune, if I may explain the situation…" His tone was typical of the condescending manner of builders and engineers even when dealing with superiors, if those superiors know less than they do of construction and mathematics.

Vitruvius cleared his throat. "Seven days ago we arrived outside Brundisium. Caesar moved at once to encircle the city and the harbor, placing the greatest part of his six legions before the city wall but also securing the promontories north and south of the harbor entrance. Our commander hoped to trap not only Pompey but also the two consuls and the many senators with him, so as to force immediate negotiations and a settlement of the crisis."

"But…" prompted Antony.

"A bad sign: our advance intelligence indicated that Pompey had assembled a considerable fleet, yet there were only a few ships in the harbor. Where had the fleet gone? Alas, before we arrived, Pompey had already sent the consuls, senators, and a substantial part of his army across the Adriatic to Dyrrachium, out of harm's way. Always seeking peace, our commander endeavored to negotiate directly with Pompey. The Great One sent back word that no lawful settlement could possibly be concluded in the absence of the consuls. Hence, no negotiations."

"Our intelligence from within Brundisium- Pompey has treated the locals with contempt and they're eager to help Caesar- informed us that Pompey kept twenty cohorts with him. Not to hold the city indefinitely- how could he, with only twelve thousand men against three times that number?- but long enough for his fleet to reach Dyrrachium, unload the first round of passengers, then return to Brundisium to pick up Pompey and his men."

"Our commander, having pursued Pompey this far, had no intention of allowing him to slip away. He came to me. 'They must be stopped, Engineer Vitruvius! We must prevent Pompey's ships from reentering the harbor when they return, or if they manage to do so, we must prevent them from leaving. But I have no ships of my own, and my men cannot march on water. This strikes me as an engineering problem, Marcus Vitruvius. Can you blockade the harbor?' I said I could. 'Then make it thus, Engineer Vitruvius!' "

The little man waved his arm in the direction of the harbor. "You can see the result from here. We began by building great breakwaters of earth and stone on either side of the harbor entrance, where the water is shallow. Unfortunately, as the work progressed and we reached deeper water, it became impossible to keep the earthworks together. At that point we built a raft, thirty feet square, at the end of each breakwater and moored each raft with anchors at all four corners to keep them still in the waves. Once these platforms were in position, we added more rafts, joined them firmly together and covered them with a causeway of earth, so that they were as steady as an actual breakwater, even though they float atop the waves. If you squint, you can see that screens and mantlets have been put up all along both sides of the causeways to protect the soldiers coming and going. On every fourth raft we constructed a tower two stories high, to defend against attacks by sea. The goal, of course, was close off the harbor completely."

Antony grunted. "All this was your idea?"

Vitruvius beamed. "Actually, if you believe the Greek historians, Xerxes the king of Persia did something like this when he bridged the Hellespont and led his army from Asia into Europe. I've always wondered how such a feat was accomplished. I suspect he must have used a similar technique, anchoring rafts and linking them together."

Meto had often told me of great feats of engineering conjured by Caesar in his battles against the Gauls. Under Caesar's command, men bridged rivers and chasms, dug vast trenches and canals and tunnels, and constructed great towers and siege engines. But an attempt to close off a harbor was something new.

Antony nodded, clearly impressed. "What was Pompey's response to all this construction? Don't tell me he watched idly from the city walls once he realized what was happening."

"Of course not," said Vitruvius. "After he stopped gaping in wonder, the Great One commandeered the largest merchant vessels remaining in the harbor and outfitted them with siege towers, three stories tall. The ships have been making sorties out to the harbor entrance every day, trying to break up our rafts. They've managed to slow the work, but not destroy it. It's been a daily spectacle, watching our towers on the rafts and their towers on the ships fire missiles and fireballs and arrows back and forth. Blood on the water… trails of reeking smoke… explosions of steam!"

Antony frowned. "But the blockade remains unfinished. The channel is still open."

Vitruvius crossed his arms and assumed the impregnable expression of every builder whose project has fallen behind deadline. "Alas, we simply didn't have time to finish, especially with Pompey's ships hectoring us. But the idea was sound! Given another five days, or even three-" Vitruvius shook his head. "And now the fleet has returned. Those are Pompey's ships you see, lining up to enter the harbor. And there! See the commandeered merchant vessels with their towers, sailing out from the city to harass our men on the rafts and run interference for the incoming ships!"

As the sun dropped behind the hills to the west, we watched the sea battle unfold. One by one Pompey's transport ships slipped through the gap in the breakwater and ran the gauntlet. Boulders flew through the air, hurled by catapults on the rafts. Most missed the mark and landed in the water, creating prodigious splashes. Some struck masts or prows, shredded sails and sent splinters flying. One catapulted stone landed squarely on the deck of a ship and appeared to break through, at least to the rowers' deck below, but the ship failed to sink.